[EXTRACTED FROM THE REPORT OE t\iE U. S. COMMTSSTONEK OE EiSH AND FISHERIES FOR 1889 TO 1S;)1. Pages 5i« to Gil.]

PLANKTONIC STUDIES:

A COMPAIUTIVE INVESTIGATION OF THE IMPORTANCE AND CONSriTLlTION OF THE PELAGIC FAUNA AND FLORA.

BY

EHISTST II.ZECi4l.

[TJa^NSriATED I3Y GEORGE WILX0:N^ EIELD.]

washingto:n': GOVERNMENT PRINTING OFFICE. 1893. G-PLANKTOMC STUDIES: A COMPARATIVE INVESTIGATION OF THE IMPORTANCE xVND CONSTITUTION OF THE PELAGIC FAUNA AND FLORA.

By Ernst H.eckel.

[Trauslated hy George Wilton Field.]

TRANSLATOR'S PREFACE.

Prof. Haeckers " Plankton Stiulien " first appeared in the Jenaische Zeitschrift., vol. XXV, first and second parts, 1890. It was immediately published in separate form by Gustav Fischer, of Jena, and attracted much attention on the Continent and in England. The subject, "a comi)arative study of the importance and constitution of the marine fauna and flora," is presented in Prof. HiTeckel's usual pleasino- style, and the work can not fail to be of value to all interested in the bio- logical sciences, to the general reader as well as to the specialist. It derives especial interest in connection with the work of the Fish Com- mission, from its broad discussion of those many important elements which enter into the food supply of all pelagic fishes, such as the mackerel and menhaden, and, considering the extensive physical inves- tigations now being conducted in our coast waters by the schooner Granipiis, its publication at the present time will prove exceedingly advantageous. The terminology used by Prof. Haeckel may at first seem formidable, but this difficulty is more fancied than real. The ^terms are formed upon correct analogies, and most of them will probably find a perma- nent place. The definite restriction of the meaning of terms is a funda- mental necessity in every science, and for the lack of this the branch of biology here considered is in a very unsatisfactory condition. The author, first of all, proposes certain terms with a definite meaning. The word "plankton," from the Greek -Xayxro^, wandering, roaming, was, I believe, first employed by Hensen in j^lace of the German "Auftrieb," to designate all plants and animals found at the surface of the ocean which are carried about involuntarily in the water. Hteckel adopts this term, but objects somewhat to the meaning at present attached to it. Particularly valuable for us is the general review which the author gives of the discovery and growth of our knowledge of this branch, 565 566 REPORT OF COMMISSIONER OF FISH AND FISHERIES. which lie names "planktology"; the distinctions which he points out between the varied constituents and distribution of the plankton; and finally his extremely valuable suggestions for further work in the field which he so justly terms "a wonder-land." In the translation .the liberty of omitting a few personal references was taken, for the reason that we in this country know very little of the facts which have called them forth. In the case of several German words it has been found necessary for the sake of clearness to use a circumlocution. For instance, I can recall no English equivalent for '' Sioffwechsel des Meeres,^'' which would con- vey its meaning in a single word. The " cycle of matter in the sea," i. e., the change of inorganic matter into vegetable and animal organic matter, and this finally again into inorganic matter, seemed the best rendering, though even this does not include all which the German term implies.

I.—HISTORICAL EXPLANATIONS.

For the great progress made in the last half century in our knowledge of organic life, we are indebted—next to the theory of development—in a great measure to the investigation of the so-called " pelagic animal world." These wonderful organisms, which live and swim at the surface of the sea and at various depths, have long aroused the interest of sea farer and naturalist, by the wealth of the manifold and strange forms, as well as by the astonishing number of individuals—these have been referred to in many old as well as in recent narratives. A considerable number of these, especially of the larger and more remarkable forms, were described and figured in the last, or in the first half of the present, century. The new and comprehensive investigation of the "pelagic world" began in the fifth decade of our century, and is therefore not yet 50 years old. Into this, as into so many other regions of biology, the great Johannes Miiller, of Berlin, equally distinguished in the realms of morphology and physiology, entered as a pioneer. He was the first who systematically and with great results carried on the "pelagic fishery by means of a fine net." In the autunui of 1845, at Helgoland, he began his celebrated investigations upon the development of echinoderms, and obtained the small pelagic larvre of the echinoderms, and other small pelagic animals living with them, as sagitta, worm larvje, etc., at first by "microscopical examination of the sea water, which was brought in" (1). This wearisome and thankless method was soon displaced by the successful use of the "fine pelagic net." In the treatise "on the general plan in the development of the echinoderms,"

Note.—Citations inclosed in parentheses which occur in the text refer to the list of publications at the end of this paper (pp. 040, 641). :

PLANKTONIC STUDIES. ^ 567

Miiller compares the different methods of obtaining- them, and chooses, above all, ''fishing- with a fine net at the snrface of the sea." He says

I liave used this method for many years witli the best results; for the advanced

stages of the swimming hirva^. and for the time of maturity and metamorphosis it is quite indis})ensable, and in no way to be repLaced.

The students who, in 1845-46, as well as in the following years, accompanied Johannes Miiller to Helgoland and Trieste (Max Miiller, Busch, Wilms, Wagener, and others) were introduced into this method of "pelagic fishery'' and into the investigation of "pelagic tow-stuff" {pelddische Aii/trieh) obtained thereby. It was soon employed at sea with excellent results by other zoologists—by T. H. Huxley, by Krolm, Leuckart, Carl Vogt, and others, and especially by the three Wiirts- burg naturalists, A. Kolliker, Heinrich Miiller, and (3. Gegenbaur, who in 1852 examined with such brilliant success the treasures of the Straits of Messina. At this time, in the beginning of the second half of our century, the astonishing wealth of interesting- and instructive forms of life which the surface of the sea offers to the naturalist first became known, and that long series of important discoveries began which in the last forty years have filled so many volumes of our rapidly increasing zoological literature. A new and inexhaustibly rich field was thus opened to zootomical and microscopical investigation, and anatomy atid physiology, organology and histology, ontogeny and systematic zoology have been advanced to a surprising degree. The investigation of the lower animals has since then been recognized as a wide field of work, whose exploration is of great significance for all branches of science and to which we owe numberless special and the most important general conclusions. The general belief of zoologists regarding the extent of this rich pelagic animal world arose as the result of the discovery that a s])ecial "pelagic fauna" exists, composed of many characteristic forms, funda- mentally different from the littoral fauna. This pelagic fauna is made uj) of animals (some floating passively, others actively swimming) which remain at the surface of the sea and never leave it, or only for a short time descend to a slight dei)th. Among such true "pelagic animals" are the radiolaria, peridinia, noctiluca, medusiie, siphonophores, cten- ophores, sagitta, pteropods, heteropods, a greater.part of the Crustacea, the larvai of echinoderms, of many worms, etc. Important changes Avere first made in the prevailing idea of the "pelagic fauna" by the remarkable discoveries of the epoch-making Challenger expedition (1873-1870). The two leaders of this, Sir Wyville Thompson and Dr. John Murray, did not limit themselves to their chief object, the general physical and biological investigation of the deep sea, but studied with equal care and perseverance the conditions of organic life at the surface of the ocean and in zones of 5G8 REPORT OF COMMISSIONER OF FISH AND FISHERIES. various depths. As the most significant general result Murray, in his "Preliminary Eeport" (187G), says: Everywhere we have found a rich organic life at and below the surface of the ocean. If living individuals are scarce at the surface, below it the tow net commonly discloses numerous forms, oven to a depth of 1,000 fathoms and more (5, p. 536). In 1875, on the journey through theKorth Pacific Ocean (from Japan to the Sandwich Islands), the extremely important fact was established that the i^elagic organisms in oceanic zones of difi'erent depths belong- to different species; fine pelagic nets (or tow nets) " on many occasions were let down even to depths of 500, 1,000, and 2,000 fathoms, and thereby were discovered many swimming organisms which had never been captured hitherto, either at the surface of the ocean or at slight depths (up to 100 fathoms below the surface)" (0, ]). 758). The most characteristic forms of these zones of different depths belong chiefly to the class of the Radiolaria^ especially to the order of the Pluvodaria. Through the investigation of the Challenger radiolaria, which occupied for ten years the greater part of my time and attention, I was led to study anew these conditions of distribution; and I reached the con- viction that the differences discovered by Murray in the pelagic fauna, at different depths of the ocean, were still more significant than he assumed, and that they had the greatest significance, not merely for the radiolaria, but also for other groups of swimming oceanic organisms. In 1881, in my ^^Enticurf eines Systems der Challenger Radiolarien,^^ p.

422, 1 distinguished three groups: («) jjelagic, living at the surface of the calm sea; {h) zonary, living in distinct zones of depth (to below

20,000 feet) ; and {c) profound (or abyssal) animals living immediately above the bottom of the deep sea. In general, the different character- istic forms correspond (to below 27,000 feet) to the different zones.

In my "General Natural History of the Radiolaria''- (4, p. 120) I have established this distinction, and have expressed my conviction that it is i)ossible, by the aid of a suitable bathygraphic net, to demonstrate many different faunal belts overlying one another in the great deep- sea zones. The existence of this "intermediate pelagic fauna," discovered by Murray, inhabiting the zones of different depths of the ocean between the surface and the deep-sea bottom, which I have briefly called " zon- ary fauna," has been decidedly contradicted by Alexander Agassiz. He claimed, on the ground of "exact experiments" carried on during the Blal

Although these negative coiichisious fi-om the so-called " exact ex- periments" of Agassiz are contradicted by the foregoing results of the Challenger investigator, yet against the latter, with some show of right, Agassiz might have raised the objection that the ''tow net" used could establish no safe conclusion.* This objection could only be finally removed by the construction of a new tow net, which could be let down closed to a certain depth, and then opened and closed again. The merit of inventing such a closible net, and of the immediate successful

use of it, belongs to two distinguished Italian naval officers : G. Pal- un)bo, commander of the Italian war corvette Vettor Pisaiii, first con- structed such a closible pelagic net or "bathygraphical zone net;" and Naval Lieutenant Gsetano Chierchia, who during the three years' voyage of the Vettor Fisaxi around the world made a very vahiable collection of pelagic animals, used the new closible net with fine results, even at

a depth of upwards of 4,000 meters (8, p. 83).

Chierchia's first trial with this "deep-sea closible net" was June 5, 1884, in the East Pacific Ocean, directly under the equator, 15° west of the Galapagos Islands. Fourteen days later, June 19, midway between the Galapagos and the Sandwich Islands, this closible net was sunk to 4,000 meters. In this and in many other trials these Italian naval officers captured an astonishing wealth of new and interesting zonary animals, whose description has for a long time busied zoologists. The collections brought back to Naples by the Vettor Pisani are, next to those of the ChaUenger, the most imi)ortant materials from the region

under coi i sideration. A few faults which pertained to Palumbo's net were soon done away with by improvements, for which we are indebted to the engineer Peter- sen and to Prof. Carl Chun, of Breslau. The latter, in 1886, made trials in the Gulf of Naples with the improved closible net which showed "a still more astonishing richness of pelagic animals in greater

* The " tow nets " used by the Challenger were the ordiuary Miiller's net (or the " fine pelagic net" of Joh. Miiller), a round bag of Miilhn- gauze or silk mull, the mouth being kejit open by a circular metallic ring. This ring is iu ordinary pelagic fishing fastened to a handle 2 or 3 meters long (like the ordinary butterfly net). While the boat moves along, the opening of this net is held at the surface in such a way that the swimming animals are taken into the bag. They remain hanging in the bottom of this, while the water passes through the narrow meshes of the net. After a time the net is carefully inverted and the tow stuff (Attftrieb) is emptied into a glass vessel filled with sea water. If one wishes to fish below the surface, the ring of the net is fastened by means of three strings, equally distant from one another, which at a point (about 1 meter distant from the opening of the net) are joined to a longer line which is sunk by weights to a definite distance, correspond- ing to the desired depth. When Murray fastened such a tow net to the deep-sea sounding line or to the long line of the deep-sea dredge, he first obtained the inhabi- tants of the " intermediate ocean zones," but he could not thereby avoid the objec- tion that, since this tow net always remained open, the contents might come from very different depths or even only from the surface. For iu

depths, and completely overthrew the assumption that an azoic layer

of water exists between the surface and the sea bottom" (15, p. 2). Chun embraced the general results of his important bathyi^elagic investiga- tions under the four following- heads:

(1) The portiou of the Mecliterrauean iuvestigated showed a ric-li pclanio fauna at the surface as well as at all depths up to 1,400 meters. (2) Pelagic animals which during the winter and spring a])pear at the surface seek deep water at the beginning of summer. (3) At greater depths occur pelagic animals whicli have hitherto beeu seldom or never observed at the surface.

(4) A number of pelagic animals also remain at the surfjic.' during tlie summer, and never sink into deep water (15, p. 44). Among the remarks which Chun made on the vertical distribution of the pelagic fauna and the astonishing plaiiktouic wealth of the depths of the sea (at 1,000 to 2,000 meters), he Justly throws out the question, "Who knows, whether in the course of time our views will not undergo a complete reversal, and whether the depths will not show themselves as the peculiar mother earth of pelagic life, from which, for the time being, swarms are sent out to tlie surface as well as to the sea bottom! There are only a few forms which can so completely adapt themselves to the changing conditions of existence at the surface that they no more seek the deeper levels " {1.% p. 40). In consequence of his obser- vations on the periodic rising and sinking of pelagic animals, Chun "can not resist the impression that from the abundance of animal life in the de])ths the surface fauna represents relatively only an advance guard of tlie whole, which sometimes to a greater, sometimes to a less extent, and occasionally completely, withdraws itself into more protected regions. Facts plainly speak for this, that the periodical wandering of pelagic animals in the vertical direction is especially conditioned by the changes in temperature. Only a few pelagic auimal groups can endure the high temperature of the surface water during the summer; the majority withdraw from the influence of tliis by sinking, and, finally, whole groups pass their life in the cool deep regions without ever rising to the surface" (15, p. 54). The general ideas which Chun had obtained by this deep-sea inves- tigation of the Mediterranean he was able to confirm for the Atlantic Ocean on a trip made in the winter of 1887-88 to the Canary Islands (10, p. 31). At this time he made the observation that the periodical wandering of pelagic animals in a vertical direction was influenced in great part by ocean currents (at the surface as well as in deep wafer), and that among other things the occurrence of the full moon exerted a significant action (10, p. 32). Chun's special observation in the sea of Orotava, upon the poverty of the Canary plankton in November and December and the sudden appearance of great numbers and many species of pelagic animals in January and February, agrees completely with the observations which I myself made twenty years before at PLANKTONIC STUDIES. 571

in the Canary island Lanzarote. I also entirely agree with Chun regard to his general views upon the chorology of the plankton, and consider his investigations upon the pelagic animal world and its rela- tion to the surface fauna as the most important contribution which planktology has received since the pioneer discoveries of the Challenger and of the Vetfor Pisaui. Entirely new aspects and methods have been introduced into pelagic biology in the last three years by Dr. Victor Hen sen, professor of phy- thoroughly siology at Kiel (9 and 22). He has for a number of years studied the conditions of life of the fauna and flora of the bay of investigation Kiel, and as a member of the commission for the scientific of the German Ocean (at Kiel) has endeavored to improve and extend an the fisheries there, and by counting the fish eggs collected to get approximate idea of the number of fish in corresponding districts (9, conclusion that it was neces- p. 2). This investigation led him to the supply of sary and possible to come nearer to the fundamental food marine animals and to determine this quantitatively. For solving this problem Hen sen invented a new mathematical method (2, p. 33). He 18S4, in constructed a new pelagic net (p. 3), and in July, company with three other naturalists of Kiel, undertook a nine-day excursion in Hebrides the North Sea and Atlantic Ocean, which was extended to the he publislied and to the Gulf Stream (57° 42' N. Lat.) (p. 30). In 1887 containing the results of this investigation in a comprehensive work many long numerical tables, "On the Determination of the Plankton, He used or the Animal and Vegetable Material found in the sea" (9). com- the term "plankton" in place of '^Auftrieh,'' the word hitherto and monly used, because this name is not sufficiently comprehensive German term ''Atiftrieh'' or ''pelagi- suitable (9, p. 1). To be sure, the ago, was in Hcher Mulder,'' introduced by Johannes Muller forty years French, and general use and has many times been used in English, as in other Italian works. But I agTee with Hensen that in this, easier flexion, scientific terms, a Greek terminus technicus, capable of of ^^Auftrieh;' and is preferable. I ado])t the term Plankton in place The w }iolc science form from it the adjective planktonic {plauMonisch). called which treats of this important division of biology is briefly ])lanktology. Hensen regards the mathematical determination of the 2)lanlcton us, standpoint. By it he the ch ief aim of planktology from a physiological of matter hopes to solve the somewhat neglected question of the cycle trial of his in the sea. For the purpose of solving this, and to make a arranged new method on a larger scale, Hensen, in the summer of 1889, liberally a more extensive expedition in the Atlantic, which was most supported by the German government and by the Berlin Acadeniy the Berlin of Sciences. The German Emperor furnished 70,000 marks; 572 REPORT OP COMMISSIONER OF FISH AND FISHERIES.

Academy gave, from tlie income of tlie Humboldt fund, 24,600 marts, and by further contributions the entire sum at the disposal of the ex- l^edition was raised to 105,600 marks—a sum never before made avail- able in Germany for a biological expedition. The new steamer Na- tional, of Kiel, was chartered for three mouths, and was fitted out " with all the admirable contrivances for obtaining i)lankton, for deep-sea fishing, and for sounding." Besides the leader of the expedition. Prof. Hensen, five other naturalists participated: the zoologists Brandt and Dahl: the botanist Schlitt; the bacteriologist Fischer; the geographer Kriimniel; and the marine artist Eichard Eschke. The voyage of the National lasted 93 days (July 7 to November 15). The course was westward through the north Atlantic (Gulf Stream, Sargasso Sea), then southward (Bermudas, Cape Verde, Ascension) to Brazil, and eastward back by the Azores. JDuring this voyage 400 casts were made, 140 with the plankton nets, 260 with other nets. Our German navy has been but little used for scientific, still less for biological, investigations; much less than the navies of England, France, Italy, Austria, and the United States. The remarkable serv- ices which many distinguished German zoologists have rendered in the last half century for the advancement of marine biology have been car- ried on almost entirely without government aid. The German govern- ment has hitherto had very little means available for this branch of science. Therefore, great was the satisfaction when, by the libei-al en- dowment of the plankton expedition of Kiel, the first step was taken for the more extensive investigation, with better apparatus, of the biol- ogy of the ocean, and for emulation of the results which the English Challenger and the Italian Ycttor Pisani had latelj' obtained in this region. Accounts have been published of the results of the plankton expedi- tion of Kiel, by Victor Hensen (22), Karl Brandt (23), E. du Bois Eey- mond (21), and Kriinimel. The essential details of these accounts have been repeatedly published in the German newspapers, to the general effect that the i)roposed goal was reached and the most important question of the plankton was happily solved. I very greatly regret that I can not agree with this favorable verdict. (1) The most impor- tant generalizations which the plankton expedition of Kiel obtained on the composition and distribution of the X)lankton in the ocean stand in sharp contradiction to all previous experience; one or the other is wrong. (2) It seems to me that Hensen has incautiously founded a number of far-reaching erroneous conclusions on very insutticient prem- ises. Finally, I am convinced that the whole method employed by Hensen for determining the plankton is utterly worthless, and that tlie general results obtained thereby are not only false, but also throw a very incorrect light on the most important problems of pelagic biology. Before I establish this dissenting opinion let me give an account of my own i)lanktonic studies and their results. PLANKTONIC STUDIES. 573

II.—PLANKTONIC STUDIES.

My own investigatious on the organisms of the plankton were begun wonderful thirty-six years ago, when I got my lirst conception of the richness of the marine fauna and iiora in the North Sea. Accepting the kind invitation of my ever-remembered teacher, Johannes Miiller, trip to Helgo- I accompanied him in the autumn of 1854 on a vacation plank- land, and was introduced by him personally into the methods of ton fishery and the investigation of the pelagic fauna. There, during August and September, I accompanied him daily on his boating trips, I received and under all conditions of the rich planktonic captures from him the most competent instruction, and pressed with corresponding eagerness into the mysteries of this wonderful world. Never will I for- get the astonishment with which I first beheld the swarms of pelagic animals which Miiller emptied by inversion of his "fine net" into a glass jar of sea water—a confused mass of elegant medusae and glistening ctenophores, swift-darting sagittas and snake-like tomopteris, copepods and schizopods, the pelagic larvre of worms and echinoderms. The important stimulus and instruction of the founder of planktonic inves- tigatio^n has exercised a constant infiuence on my entire later life, and has given me a lasting interest in this branch of biology.* Two years later (in August and September, 185G), while at Wiirtz- burg, I accepted the invitation of my honored teacher, A. Kolliker, to accompany him to Mzza, and, under his excellent guidance, became acquainted with the zoological treasures of the Mediterranean. In ct)mpauy with Heinrich Miiller and K. Knpfifer, Ave investigated espe- cially the rich pelagic aninnil life of the beautiful bay of Villafranca. Tliere, for the first time, I met those wonderful forms of the pelagic fauna which beh)ng to the classes of the siphonophores, pteropods, and heteropods. I also there first saw living polycyttaria, acanthometra, and polycystina, those phantasmic forms of radiolaria, in the study of which I spent so many later years. Johannes Miiller, who was at this time at Nizza, and had already begun his special investigation of this latter order, called my attention to the many and important questions which the natural history of these enigmatical microscopical organisms present. These valuable suggestions resulted some years later in my going to Italy and spend- ing an entire year in pelagic fishing on the Mediterranean coast. Dur-

* When at Helgoland, investigating the wonders of the plankton with the micro- his zealous scope, Johannes Miiller, pleased with the care and patience Avith which students tried to study the charming forms of meduste and ctenophores, spoke to me have the ever-memorable words, "Tliere you can do much; and as soon as you entered into this pelagic wonderland you will see that you can not leave it." 574 REPORT OF COMMISSIONER OF FISH AND FISHERIES. iDg the summer of 1859, at Naples aud at Oapri, I endeavored to gain as wide a knowledge as possible of the marine fauna. In the following winter, at Messina, I devoted my entire attention to the investigation of the radiolaria, and thus obtained the material which forms the basis of my monograph of this class (1802). Daily boat trips in the harbor of Messina made me acquainted with all the forms in the pelagic fauna which make this classic spot, in consequence of the com- bination of uncommonly favorable conditions, far richer for planktonic study and investigation than any other point on the Mediterranean

(3, pp. v, 25, 166, 170). For a full generation, since that time, the study of plankton has remained my most i^leasant occupation, and I have haidly let a year pass without going to the seacoast and, by means of the j)elagic net, getting new material for work. Various inducements were offered to me in addition ; on the one hand the radiolaria, on the other the siphouo- phores aud medusie, to which I had already given some attention while at Mzza in 1864. The results of these studies are given in my mono- graphs of these two classes (1870 and 1888). In the course of these three decades I have by degrees become acquainted with the entire coast of the Mediterranean and its fauna. I have already made reference, in the preface to my "System of Medusae," p. xvi, to the places where I have studied this subject. In addition to the Mediterranean I iave continued my planktonic studies on the west coast of Norway (1869) ; on the Atlantic coast of France (1878); on the British coast (1876 and 1879); at the Canary Islands (1866-67); in the Eed Sea (1873), and in the Indian Ocean (1881-82). By far my richest results and my deepest insight into the biology of the plankton were vouchsafed me during a three months' residence at Puerto del Arrecife, the seaport of the Canary island Lanzarote (in December, 1886, and in January and February, 1887). The pelagic fauna in this part of the Atlantic is so rich in genera and species; the fabulous wealth of life in the wonderful "animal roads" or Zain currents (18, p. 309) is, every day, so great, aud the opportunities for investigation on the spot are so favorable that Lanzarote afibrded me greater advantages for planktonic study than all the other places ever visited by me (excepting perhaps Messina). Every day the pelagic net brought to me and to my companions (Prof. Eichard Greeff" and my two students, N. Miklucho-Maclay and H. Fol) such quanti- ties of valuable tow-stufi' {Auftrieh) that we were able to work up only a very small part of it. At that time I concentrated my chief inter- est on the medusae and siphonophores, and the larger part of the new material which is worked up in my monographs of these two classes was collected at Lanzarote. All my observations "On the Development of the Siphonophores" (1869) were made there. PLANKTONIC i^TUDIES. 575

The excursiou to the coral reefs of the Red Sea (1873), which is recounted in my ''Arabic Corals," and the trip to Ceylon, about which I have written in my "Indian Journal" {Indische Eeisehriefe, 1882), were extremely valuable to me, because I thereby gained an insight into the wonders of the Indian fauna and flora. On the journey from Suez to Bombay (in Js^ovember, 1881), as well as on the return from Colombo to Aden (in March, 1882), I was able to make interesting observations on the pelagic fauna of the Indian Ocean, as well as dur- ing a six weeks' stay at Belligam and in the pelagic excursions which I made from there, I obtained thereby a living picture of the oceanic and neritic fauna of the Indo-Paciflc region, which differs in so many respects fi'om that of the Atlantic-Mediterranean region. The special results of my experience there are, with the kind consent of Dr. John Murray, for the most part embraced in my report on the Radiolaria (1887), and on the Siphonophora (1888), which form parts xviii and XXVIII of the ChaUemjer Report. These two monographic reports also contain many observations on plankton, which I had made in earlier journeys and had not yet published. The extensive experience which I had gained through my own obser- vations of living plankton during a period of three decades was well filled out by the investigation of the large and well-preserved planktonic collections placed at my disposal from two different sources by Capt. Heinrich Rabbe, of Bremen, and by the Challenf/er directors of Edin- burgh. Capt. Rabbe, with very great liberality, turned over to me the valuable collection of pelagic animals which he had obtained on three different trips (with the ship Joseph Raydn, of Bremen) in the Atlantic, Indian, and Pacific oceans, and which he had carefully preserved according to my directions and by approved methods. This extraor- dinarily rich and valuable material, contained in numerous bottles, embraced planktonic samples from the most diverse localities of the three oceans, chiefly in the southern hemisphere. Like the nuich more extensive collection of the ChaUemjer, it gives (though to a smaller degree) a complete summary of the complexity of the composition of the plankton and the difference in its constituents. Rabbe's collection supplements that of the Challenger in a most welcome manner, since the course of the Challenger was southward from the Indian Ocean through the Antarctic region, and between the Cape of Good Hope and Mel- bourne was always south of 40° south latitude. The course of the Joseph Haydn, on the other hand, on the repeated voyages through the Indian Ocean, was much more northerly, and between Madagascar, the Cocos Islands, and Sumatra included a number of points where the pelagic net obtained a very rich and peculiarly constituted capture. I hope to be able to publish soon in detail the special results which I have obtained by investigation of Rabbe's plankton collection, with the aid of the ^carefully kept journal which Capt. Rabbe made of liis observa- tions. The discoveries of new radiolaria, medusie, and siphonophores 576 REPORT OF COMMISSIONER OF FISH AND FISHERIES. which I owe to these are ah-eady embraced in my monographs on these three classes in the Challenger Eeport, and in the preface I have ex- jiressed to Gapt. Eabbe my sincere thanks for his very vahiable aid. Of all expeditions which have been sent out for investigating the biology of the ocean, that of the Challenger was, without doubt, the greatest and the most fruitful, and I recognize it with additional grati- tude since I was permitted for twelve years to take part in working up its wonderful material. When, after the return of the expedition, I was honored by its leader. Sir Wyvillc Thompson, by being summoned to work up the extensive collection of radiolaria, I believed, after a hasty survey of the treasures, that I could complete their investigation in the course of three to five years; but the further I proceeded in the inves- tigation the greater seemed the assemblage of new forms (4, p. xv), and it was a whole decade before the report on the radiolaria (part xviii) was completed. Three other reports were also then finished—on deep- sea horny sponges (part lxxxii), on the deep-sea medusiT3 (part xii), and on the siphonophores (part xxviii) collected by the Challenger. The comparative study of these extremely rich planktonic treasures was highly interesting and instructive, not only on account of the daily additions to the number of new forms of organisms in these classes, but also because ray general ideas on the formation, composition, and importance of the plankton were enriched and extended. I am sin- cerely thankful for the liberality with which Sir Wyville Thomi^son, and after his untimely death (1882) his successor. Dr. John Murray, placed these at my entire disposal. A record of the 168 stations of observations of the Challenger ex- pedition, whose soundings, plankton results, and surface preparations

I have been able to investigate, has been given in § 240 of the report on the radiolaria (4, p. clx). The number of the bottles containing plankton (from all parts of the ocean) in alcohol amounts to more than a hundred, and in addition there are a great number of wonderful preparations which Dr. John Murray finished at the different obser- vation stations, stained with carmine and mounted in Canada balsam. A single such preparation ^for example, from station 271) contains often 20 to 30 and sometimes over 50 new species. Since the material for these preparations was taken with the tow net, not only from the surface of all parts of the sea traveled by the Challenger, but also from zones of different dej^ths, they make important disclosures in morphol- ogy as well as in jihysiology and chorology. To the study of these station preparations I am indebted for many new discoveries. I have been able to examine over a thousand (4, p. 16). If I here refer to the development and extension of my own plankton studies, it is because I feel compelled to make the following brief sum- mary of results. I am not now in a position to give the proofs in detail, and must defer the thorough establishment of the most weighty PLANKTONIC STUDIES. 577

series of observations for a later and more detailed work. But since, to my regret, I am compelled to decidedlj' contradict the far-reacliing assertions made by Hensen (22), it is only to justify and prove these that I refer to my extended experience of many years. I believe I do not err in the assumption that among living naturalists I am one of those who by extensive investigation on the spot have become most thoroughly acquainted with the conditions of the plankton and have worked deepest into these intricate problems of marine biology. If I had not for so many years hud these continually in mind, and at each new visit to the sea begun them anew, I would not dare to defend with such determination the assertions expressed in the following pages.

III.—CHOROLOGICAL TERMINOLOGY.

The science of the distribution and division of organic life in the sea (marine chorology) has in the last decade made astonishing progress. Still this new branch of biology stands far behind the closely related terrestrial chorology, the topography and geography of land-dwelling organisms. We have as yet no single work which treats distinctly and comprehensively of the chorology of marine plants and animals in a manner similar to Griesbach's <' Vegetation of the Earth" (1872) for the land jilants, and Wallace's "Geogra])hical Distribution of Animals" (187G) for the land animals. How much there is still to be done is shown by the fact that not one of the simplest fundamental conceptions of marine chorology has yet been established. For example, the most important conception of one subject, that of the pelagic fauna and flora, is now employed in three different senses. Originally, and through several decades, this term was used only in the sense in which Johannes Miiller used it, for ani- mals and plants which are found swimming at the surface of the sea. Then the term was extended to all the different animals and plants which are found at the surface of fresh- water basins. It was so used, for example, by A, Weismann in his lecture upon " the animal life at the sea-bottom" (1877), in which he "distinguishes the animal world living on the shore from the 'pelagic or oceanic company living in the open sea.'" To a third quite different meaning has the conception of the pelagic living world been widened by Chun (1887), who extends it from the surface of the ocean down to the greatest depths (15, p. 45). In this sense the conception of the pelagic organisms practically agrees with the "plankton" of Hensen. Errors have already arisen from the varied use of such a funda- mental conception, and it seems necessary to attempt to clear this up, and to establish at least the most important fundamental conception of marine chorology. In the use of words I will, as far as possible, conform to the usage of the better authors. H. Mis. 113 37 578 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

MARINE FLORA AND FAUNA.

Since the old mooted question about "the limits of the animal and vegetable kingdom " comes anew into the foreground in the planktonic studies, a few words must first be devoted to its consideration. In the plankton, those organisms (for the most i)art microscopic) which stand on the boundary liue and which may be regarded as examples of a neutral "Protista realm," play a conspicuous part—the unicellular diatoms and murracytes, dictyochea and palmellaria, thalamophora and radiolaria, dinoflagellata and cystoflagellata. Since it is still asserted that for replies to this boundary question we need new researches, "more exact observations and experiments," I must here express the opposing belief, that the desired answer is not to be obtained by this empirical and inductive method, but only by the philosophic and deduct- ive method of more logical definite conception {logisclier Begriff-Bestim- mung). Either we must use as a definite distinction between the two great organic realms the physiological antithesis of assimilation, and consider as "plants" all "reducing organisms" (with chemical-synthetic functions) and as "animals" all "oxidizing organisms" (with chemical- analytical functions) or we may lay greater weight on the morphological differences of bodily structure and place the unicellular ''Protista'''' (with- out tissues) over against the multicellular Histona (with tissues).* For the problem before us, and with more particular reference to the questions of the fundamental food suj)ply Urnahrung) and important ( the cycle of matter in the sea {Stoffwechsel des Meeres), it is here more suitable to employ the first method. I regard the diatoms, murracytes, and dinoflagellates as Protoplujtes^ the thalamophores, radiolarians, and cystoflagellates as Protozoa. For a term to designate the totality of the marine flora and fauna, the expre>ssion halohios seems to be suitable, in opposition to Uunwbios (the organic world of fresh water) and to geohios (as the totality of the land-dwelling or terrestrial plant and animal world). The term hios was applied by the father of natural history, Aristotle, "to the whole world of living " as opposed to the lifeless forms, the ahion. The term biology should be used only in this comprehensive sense, for the whole organic natural science, as oi)posed to the inorganic, the abiology. In this sense, zoology and botany on the one side, and morphology and physiology on the other, are only subordinate parts of biology, the general science of organisms. But if (as is frequently done to-day even in Germany) the term biology is used in a much narrower sense, instead of(»co/o;7^, this narrowingleads to misunderstandings. I mention

^ rrotlsta aud Hiaiona may both again be divided into two groups, on the ground of the different assimilation, into an auimial and a vegetable group, the Protista into Protophrita and Protozoa, the Histona into Metaplnjta aud Metazoa. Compare my "Natural History of Creation" (XatUrliche Schopfungsijeschichte), 8th edition, 1889, pp. 420 aud 453. TLANKTONIC STUDIES. 579 this here because iu plauktology the interesting- and complex vital relations of pelagic organisms, their manner of life and economy, are very often called biological instead of cecological problems.*

PLANKTON AND BENTHOS.

If under the term Halohios we embrace the totality of all organisms living iu the sea, then these, in (ecological relation, fall into two great chief groups, benthos and pJc.nkton. I give the term lenthos] (in opposi- tion to plankton) to all the nou-swimining organisms of the sea, and to all animals and plants which remain upon the sea bottom either lixed (sessile) or capable of freely changing- their place by creeping or run- ning (vagrant). The great ojcological differences in the entire mode of life, and consequently in form, which exist between the benthonic and planktonic organisms, justify this intelligible distinction, though here as elsewhere a sharp limit is not to be drawn. The hentJios can itself be divided into littoral and abyssal. The littoral-benthos embraces the sessile and vagrant marine animals of the coast, as well as all the plants fixed to the sea-bottom. The ahyssal-benthos, on the other hand, comprises all the fixed or creeping- (but not the swimming) ani- mals of the deep sea. Although as a whole tlie morphological char- acter of the benthos, corresponding to the i)hysiological peculiarities of the mode of life,, is very different from that of the plankton, still these two chief groups of the halobios stand in manifold and intimate correlation to one another. In part these relations are only phylo- genetic, but also in part at the i^resent day of an ontogenetic nature, as, for example, the alternationof generations of the benthonic polyps and the planktonic medusiL\ The adai)tation of marine organisms to the mode of life and the organization conditioned thereby may in both chief groups be primary or secondary. These and other relations, as, well as the general characteristics of the |)elagic fauna and tlora, have already been thoroughly considered by Fuchs(lL') andMoseley(7).

PLANKTON AND NEKTON.

The term fiankton may be used in a wider and in a narrower sense; either we understand it as embracing all organisms swimming in the sea, those floating passively and those actively swimming; or we may exclude these latter. Hensen comprehends under plankton " every- thing which is in the water, whether near the surface or far down, whether dead or living." The distinction is, v>hether the animals are driven involuntarily with the water or whether they dis])lay a certain degree of independence of this impetus. Fishes in the form of eggs

* The terms biology and cecology are not intercliangeable, because the latter only

forms a part of physiology. Comp. my " Generelle Morphologie," 1866, Bd. i, j). 8, 21; Bd. II, p. 286; also my ''Ueber Etwickelungsgang und Aufgabe der Zoologie/'' Jena. Zeitsch. fur Med. u. Nat., Bd. v, 1870. t/ieVQo?, the bottom of the ocean; hence the organisms living there. 580 REPORT OF COMMISSIONER OF FISH AND FISHERIES. and young belong in the highest degree to the plankton, but not when mature animals. The copepods, although lively swimmers, are tossed about involuntarily by the water, and, therefore, must be reckoned in the plankton (9, p. 1). If, with Henseu, we thus limit the conception of 2)Ianldon, then we must distinguish the aetirely swimming nelcton from the passivehj driven iilanldon. The teiin thus loses its firm hold, and becomes dependent on quite variable conditions; upon the changing force of the current in which the animal is driven, by the momentaiy energy of voluntary swimming movements, etc. A pehigic fish or copepod, which is borne along by a strong current, belongs to the plankton ; if he can make a little i)rogress across this current, and if, besides this, he can voluntarily and iudependently define his course, then he belongs also to the nekton. It therefore seems to me advisable, as jireliminary, to regard the term plankton in the wider sense, in oi)j)0- sition to benthos. Still, for the chief theme which Hensen has set up in his plankton studies, for the physiological investigation of the cycle of matter in the sea {Stofffwechscl des 3Ieeres), this limitation of the plankton con- ception will not hold; for a single large fish which daily devours hun- dreds of i)teropods or thousands of coi)epods exerts a greater intluence on the economy of the sea than the hundreds of small animals which belong to the i)lankton. I will return to this in speaking of the vertebrates of the i)lankton. If with Hensen we could, on practical grounds, separate those animals of the plankton which are carried involuntarily from those following their own voluntary swimming movements (independent of the current), we might distinguish the former as ploteric* the latter as nccferic*

HALIPLANKTON AND LIMNOPLANKTON.

Although the swimnung population of fresh water shows far less variety and i)eculiarity than that of the sea, still among the former as among the latter similar conditions are develoi^ed. Already the study begins to take a joyous flight to the pelagic animals of the mountain lakes, etc. Therefore, it will be necessary here also to fix limits, as has been already done for the marine fauna; but since the term "pelagic" should only be used for marine animals, it becomes advis- able to designate as limnetic the so-called "pelagic" animals of fresh w\ater. Among these we can again distinguish auioJimnetic (living only at the surface), zonolimnetic (limited to certain depths), and haihylim- netic (dwellers in the deep waters). The totality of the swimming and floating population of the fresh water may be called Jimnoplanldov, as opposed to the marine liaUpJanMon (9, p. 1), Avhich we here briefly <-A\\\pJ(tnldon.

* Tl/io>-//p = drifting ; vtiktij^ = swimming, PLANKT0^^1C STUDIES. 581

OCEANIC Ai^D NERITIC* PLANKTON.

The manifold differenees wliicli the character of the plimlcton shows according to its distribution in the sea, lead first, with reference to its horizontal extension, to a distiuction between oceanic and neritic plankton. Oceanic pkmlion is that of the open ocean, exclusive of the swiinniing" bios of the coast. The rejiion of oceanic plauktou may froui a zoological point of view be divided into five great provinces : (1) the Arc- ticOcean; (2) the Atlantic; (.3) the Indian; (4) the Pacific; (5) the Ant- arctic. In each of these five great provinces the characteristic genera of the plankton are apparent through the different species, even if the differences in general are not so significant as in the different provinces of the neritic and still more of the littoral fauna. The neritic i)lankton embraces the swimming fauna and fiora of the coast regions of the continents as well as the archipelagos and islands. This is in its composition essentially different from the oceanic plank- ton, and is quantitatively as well as (|ualitative]y richer. For along the coast there develop, partly under i)rotection of the littoral bios, or in genetic relation with it, numerous swimming animal and vegetable forms which do not generally occur in the open ocean, or there quickly die; but the fioating organisms of the latter may be driven by currents or storms to the coast and there mingled with the neritic plankton. Aside from this the richness of the neritic plankton in genera and species is much greater than that of the oceanic. The complicated and manifold relations of the latter to the former, as well as the relations of both to the benthos (littoral as well as abyssal), have been but little investigated and contain a fund of interesting problems. One could designate the neritic plankton also as "littoral plankton" if it were not better to limit the concei)tion of the littoral bios to the non-swimming organisms of the coast, the vagrant and sessile forms.

PELAGrIC, ZONARY, AND BATHYBTC PLANKTON.

I keep the original meaning of the pelagic planJdon as given forty -five years ago by Johannes Miiller, and used since by the great majority of authors. I also limit the meaning of the pelagic fauna and flora to those actively swimming or passively floating animals and plants, which are taken swimming at the surfiice of the sea, no matter whether they are found here alone or also at a variable depth below the surface.

These are the superficial and interzonary organisms of Chun (15, p. 54). On the other hand, I distinguish the zonary and bathybic organisms; I call zonary planldon those organisms which occur oidy in zones of defi- nite depths of the ocean, and above this (at the surface of the sea) or below (at the sea bottom) are only found occasionally, as for example many phajodaria and Crustacea; also the deep-sea siphonophores dis-

* Nr/piriji, sou of Nereiis. —;

582 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

covered by Chiercliia, wliicli were taken by him in great numbers and in great vertical and horizontal extension, but never higher than 1,000 meters below the surface and never deeper than 1,000 meters above the sea bottom (8, p. 85). The deepest part of this zonary fauna forms the haihyhic planMon (or the profound tow-stuil", A<(/ifWe6), i. e., animals of the deep sea, which only hover over the bottom but never touch it, whether they stand iu definite relation to the abyssal benthos or not.

One might also call them ^' abyssal planT

AUTOPELA.GIC, BATHYPELAGIC, AND SPANIPELAGIC PLANKTON.

If, following the old custom, we limit the term "pelagic hios''^ to those organisms wliich, at some time, swim or float at the surface of the sea if we do not with Chun (15, p. 45) extend this term to the zonary and bathybic animals—it still is necessary to further distinguish by differ- ent terms those forms of life which constantly, temporarily, or only exceptionally live at the surface of the sea. I suggest for these the terms autoj^elagic, bathypelagic, and sijanipelagic. Autopelagic are those animals and plants which are constantly found only at the sur- face (or iu stormy weather at slight depths below it), the "superficial" of Chun (15, pp. 45, 60). To this "constant superficial fauna" belong, for example, many polycyttaria (most sphiierozoids), many medusae (e. r/.,

Encoplda'), and many sii^honophores {e. g., ForsJcalicIa'); further, the lobate ctenophores {Eucharis, BoUna), particular species of Sagitta {e.

hipunctnta)^ and many copepods [e.

Moseley (7), Chierchia (8), and Chun (15, 16), as well as from my own wide experience, it becomes highly probable that the great number of pelagic animals and plants only pass a part of their lives at the surface swimming at different depths during the other part. Among the bathypelagic animals there are farther to be distinguished: (a) Kycti- 2)elagiCj which arise to the surfiice only at night, living in the depths during the day; very many meduste, siphonophores, pyrosoma, most PLANKTONIC STUDIES, 583

licterupods, very many Crustacea, etc. (/>) Chimopekujic, pteropods, and ; whicli appear at tlie surface only in winter and in summer are bidden in the depths—radioiaria, medusa', siphouophores, ctenophores, a part of the pteropods and heteropods, many Crustacea, etc.; (c) Allopehujic, which perform irregular vertical wanderings, sometimes appearing at the surface, sometimes in the depths, independently of the changes of temperature, which condition the change of abode of the nyctipelagic and chimopelagic animals; the final cause of these wanderings ought to be found in different oecological conditions, as of reproduction, of outogeny, of food supply, etc. Finally one may call spanipelagic those animals which always live in the ocean dejiths (zonary orbathybic), and come to the surface only exceptionally and rarely. This does not apply to a few dee])-sea ani- mals which once every year ascend to the surface, but only for a short time, for a few weeks or perhaps I'or a single day, c. g., Athoryhia and PhysopJiora among the siphonophores, Charybdea und Per ijjhylla among the medusie. The final cause of this remarkable spanipelagic mode of life must lie chiefly in the conditions of reproduction and ontogeuy. These animals must be much more numerous than present appearances show.

HOLOPLANKTONIC AND MEEOPLANKTONIC OEGANISMS.

Numerous organisms pass their whole life and whole cycle of devel- opment hovering in the ocean, while with others this is not the case. Tliese rather pass a ]>art of their life in the benthos, either vagrant or sessile. The first groiip we call holoplanldonic^ and the second mero- pJanMonic. To the holoplanktonic organisms, which have no relation whatever to the benthos, belong* the greater part of the diatoms and oscillaria, all murracytes and peridinea; further all radiolaria, many globigerina, the hypogenetic medusie (witliout alternation of genera- tions), all siphonophores and ctenophores, all chsetognatha^, pteropods, the copelata, pyrosoma, and thalidia„etc. Among these we find '^purely pelagic, zonary, or bathybic*' forms. The meroplanlctonic organisms, on the othei- hand, which are found swimming in the sea only for a part of their life, passing the other part vagrant or sessile in the benthos (either littoral or abyssal), are represented by the following groups: A x:)art of the diatoms and oscil- laria, the planktonic/?/con7,9, the metagenetic medusre {Cras2)edotawit]i hydroid nurse, Acraspeda with scyphistoma nurse), some turbellariaus and annelids, etc; further, the "pelagic larva;" of hydroids and corals, many helminths and echinoderms, acephala and gasteropods, etc. 584 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

IV.—SUMMARY OF THE PLANKTONIC ORGANISMS.

A. —riionjPllYTKS OK TIIK PLANKTON.

The vniceUnJiir plants {Protopliyta*) have very great importance

ill the physiology of the phinktoii and the cycle of matter in the sea {^ioffweclisel des Meercs), for they furnish by far the greater part of the fundamental food {Uniahrung). The inconceivable amount of food which the countless myriads of swimming marine animals consume daily is chiefly derived, directly or indirectly, from the planlctonic flora, and in this the unicellular protophytes are of much greater importance than the multicellular metaphytes. Nevertheless the natural history of these small plants has thus far been very much neglected. As yet no botanist has attemi)ted to consider the planktonic flora in general, and its relation to the planktonic fauna. Only that single class, so rich in forms, the diatoms, has been thoroughly investigated and .systemat- ically worked up; as regards the other groui>s, not a single attempt at systemization has been made; and many simple forms of great impor- tance have lately been recognized for the first time as unicellular plants. I must, therefore, limit myself here to a brief enumeration of the most important groups of the plankton flora. Its general extent and quanti- tative development have in my opiniou hitherto been much under- valued, and with reference to the cycle of matter in the sea {StaffwecJtsel (les Meeres) deserve a thorough consideration. I find masses of various protophytes everywhere in the plankton, and suspect that they have been neglected chiefly because of their small size and inconspicuous form. ]\rany of these, indeed, have been regarded as protozoa or as eggs of planktonic metazoa. As a foundation for a most important province of botany, the classi- fication of the protoi)hytes, we must kee]) in the foreground the follow- ing considerations: (1) The kind of reproducticm, whether by simple division {Schizophyta) into two, four, or many parts, or by formation of motile swarm-spores, Ma.stigopln/fa: (2) the constitution of the i)hy- tochroms, of yellow, red, or brown pigment, which is distributed in the protoidasm of the cell (usually in the form of granules), and has great significance in assimilation (chlorophyll, diatomin, erethrin, i>h;eodin, etc.); (3) the morphological and chemical constitution of the cell-mem- hrane (cellulose, siliceous, capsular, or bivalvular, etc.). So long as we hold to the present view of the vegetable physiologists, that for the fundamental process of vegetal assimilation, for the synthesis of proto- plasm and amylum, the presence of the vegetal pigment matter is nec- essary, we can regard as true protophytes only such unicellular organ- isms as are provided with such a phytochrom, but we will have to

* The separation of tlie Protopliyta from the Metaphyta is as justifiable as that of the Protozoa from the Metazoa. The latter form tissues, the former do not. (Compare Natiirl. Sc'ho])fungsgesohichte, viii Aufl., 1889, jtp. 420-453.) .

PLANKTONIC STUDIES. 585

include here a great number of protista, which have hitherto been

reckoned as protozoa, e. //., the Murraci/tea', Diciyochew, Fcridinea'. As characteristic and important protopliytes of the plankton I here

mention seveiii groups: (1) Chromacea', (2) Calcocytea'j (3) Ifnrracytecv,

(4) iJiatomea', (5) Xanthellea', (G) Dictyochea', (7) Feridinea'. 1 Chromacece (30, p. 452).—In this lowest vegetable group is probably to be placed a number of snmll "unicellular alg.e" of simplest form, which occur in great abundance in the jjlankton, but on account pt their minute size and simple spherical shape have for the most part been overlooked, or possibly regarded as geiin cells of other organisms. They may here be i)rovisionally distinguished as FrocyteUa 2)>'imordi((Us. The diameter of the spherical cells in the smaller forms is only about .001 to .005 mm., in the larger .008 to .012 mm, seldom more. Usuallj^ each cell contains only one phytochrom granule of greenish color, sometimes approaching a yellow or red, sometimes a blue or brown. Whether there is also a diminutive nucleus is doubtful. Increase takes l»lace simply by division into two or four parts, and appears to go on with excessive rapidity, but swarm si^ores do not appear to be formed. Hundreds or thousands of such green spheres may be united in a mass of jelly. The decision whether these simplest Chromacece belong to the Chlorcoccecv or Frotococcea', or to some other primitive protophytic group, nmst be left to the botanist for further investigation, as well as the (|uestion whether these diminutive FrocyteUw are actually true nucleated cells or only unnucleated cytodes. For our plankton studies these are of interest only so far as they develoj) in astonishing quantities in manj- (the colder) regions of the ocean, like the diatoms; and with the latter form a great part of the fundamental food {Uniahrung). Over wide areas the sea is often colored brown or green, and they form the chief food (described as Frotococcus marinus) of inconceivable myriads of copepods, as Kiikenthal has mentione

2. Calcocytew.—In the eighth edition of the ^'- Naturliche Scliopfnngs- geschichte''^ (30, p. 437) I have designated as Calcocytew or "unicellular calcareous algie " those imj^ortant minute organisms which, as " Coc- cosplmra^ Cyathosphcera, and Bliahdospltwra, play a great role in oceanic life. They are found abundantly in the plankton of the tropical and sul)tropical seas, less abundantly in colder zones, and are never absent where pelagic Thalamophora occur in great numbers. Like the latter,

they arebathypelagic. Theball of protoplasm which completely fills the interior of the small calcareous-shelled plastid seems, when stained red with carmine or brown with iodine, to be unnucleated, and therefore a tode. beautiful shell Cocco- cy The calcareous plates which comj^ose the ( litha, Cyatholitha, Bhahdolitha), and which in the RhahdosplKera bear a radial spine, fall apart after death and are found in great numbers in all parts of the warmer oceans and in the globigerimi ooze of the bottom.

Murray (5, p. 533; G, p. 939) and Wyville Thompson (14, i, p. 222) :

586 REPORT OF COMMISSIONER OF FISH AND FISHERIES. were the first to demonstrate tlie wide distribution and innumerable abundance of this unicellular calcareous alga, and I agree with them in tlie supposition that these play a significant part in the biology of the ocean and in the formation of its globigerina ooze. 3. Murracytecv.—TJBcler this name I may here refer to tlie very im- portant but hitherto neglected group of planktonic protophytes, which were first discovered by John Murray and described under the name Pyroeystis (5, p. 533, plate xxi; 6, pp. 935^938). These '^ unicellular algcT3"are transparent vesicles, from 0.5 to 1 or 1.5 millimeters in di- ameter, and spherical, oval, or spindle-shaped in form. Their simple continuous cell membrane is veiy thin and fragile, like glass. It is stained blue by iodine and sulphuric acid, and seems to contain a small quantity of siliceous earth. The contents of the vesicle is a vacuolated cell, whose protoplasmic network contains many yellow granules of diatomin. The spherical form {Pyroeystis noctiluca Murray) is very similar in size and form to the connnon NoGtiluca miliar is and probably is very often mistaken for it. I saw these thirty years ago (1860) at Messina, and later (1866) at Lanzarote, in the Canary Islands. AVhen John Murray published in 1876 the first figures and careful description, he at first placed them with the diatoms, but later (6, p. 935) he has, with justice, separated them. He there says of Pyroeystis noctiluca This organism is everywhere present, often in enormous masses, .at the surface of the tropical and subtropical oceans, where the temperature is not more than 20^ to 21° C and the specific gravity of the oceanic water is not diminished by the presence of coast and river water. Pyroeystis shines very brightly ; the light comes from the nucleus and is the chief source of the diffuse phosphorescence of the equatorial oceans in calm Aveather.

Since tliese unicellular vegetable organisms do not have the char- acteristic bivalve shell or siliceous case of the diatoms, but their cell membrane forms a completely closed capsule, they can not be reckoned with the latter, but must lie regarded as representatives of a different group of protophytes, for which I propose the name Murracytecv or "glass bladders" {Murra, a name given by the Eomans to a glasslike mmeral-fluospar(?)— from which costly articles are made.)*

nn the Atlantic and Indijin oceans I h'^i^^seen great masses of M^^^^^^Zy^^a^i have dis inguished many species, which may be regarded as representatives of four genera: (1) P^,.ocv.s/is „oe/l/«,ca Murray; spherical. (2) Fhotoc„stls elllpsoldes Hkl- "^'^ (pyroeystis fuslformls Murray); spindle: Bhrer\4?\shaped, (i) r^T''-^'"'-^"''"" ^eetacyst,s .H»rm.,««« Hid; cylindrical. The Murracytes mnltLy as

eccentrically ^ or against the cell will, hal dWided *he:eheie folowsf 1 "r"'division '^fof the soft cell body, which is separated from thejjfilfirm capsulelike membrane by a wide space (filled with membrane a iellv). Then the bursts, and around the two halves or four tetrads there is immed atdv formed a new covering. ' Considered phylogenetically, the ^.r.aov/rrpear very old oceanic Protopkytes of very simple structure!^' Perhaps they regarded ought to 1 as the ancestral form of the diatoms, for the bivalvular shell of ^h latt could have arisen by a simple halving of the -apsnle of the former PLANKTONIC STUDIES. 587

in wliicli the diatoms 4. .DkUomeic—The iucoiiceiviiblc (luaiitities they populate the whole ocean and the extraordinaiT importance which possess as one of the most important constituents of the "fundamental has been food supply" {Uniahrimg) in the cycle of matter in the sea the com- considered so many times that it is sufficient here to point to etc.), Fuchs paratively recent accounts of Murray (o, p. 533; G, p. 737, and Ilensen p. 80). Earlier the (12, p. 49), Castracane (6, p. 1)30), (9, everywhere chief attention was paid to the benthonic diatoms which in aston- cover the seacoast and the shallow depths of the sea bottom among ishing quantities; in part lixed on stalks, in part slowly movhig {festsitzenden Thicr- tlie forests of seaweed and the fixed animal banks diatoms was hanlcen) of the coast. The importance of the planktonic recognized much later, those abounding in the open ocean as well as in sources of food the coast waters furnishing one of the most important often cover the sur- for the pelagic animals. The oceanic diatoms, which another flora, very face of the open sea as a thick layer of slime, form colossal size insufficiently studied and characterized by many forms of in form, and with (several millimeters in diameter), peculiarly regular extremely thin-walled siliceous shells (species of mhmodiscus, Coscino- by the Challenger). disciis, Bhizosolenia, etc., discovered in such numbers swimming free in no The neritic diatoms, on the other hand, which, with small numbers, populate the coast waters, are less in diameter and thicker walls, and stand on the whole between the oceanic and littoral planktonic diatoms forms. The absolute and relative quantity of the both poles. seems to increase gradually from the equator towards less developed In the tropical zone the pelagic diatoms are much less than in the polar than in the temperate zone, and here again much often changed by incon- zone. Wide stretches of the Arctic Ocean are water," ceivable masses of diatoms into a thick dark slime, the "black which forms the feeding-gr(mnd of whales. The pteropods and crus- slime, taceans, upon which these cetaceans live, feed upon this diatom wonderful are the the "black water" of the Arctic voyager. Not less south of the vast masses of diatoms which fill the Antarctic Ocean shells, sinking to the fiftieth degree of latitude, and whose siliceous ooze. {Ch alien (jer, bottom after the death of the organism, form the diatom with such stations 152-157). The tow nets here were quickly filled that these masses of diatoms (for the most part composed of Chcvtoceros) when dried in the oven formed a thick matted felt ((>, p. 920). cycle of matter in the 5. Xanthelle(V.—A highly important share in the live ^ea belongs to the remarkable xanthcllecc or "yellow cells," which the plankton as in si/mhiosis in the bodies of many marine animals, in "yellow cells," which iveli as in the benthos. I first proved that these were observed by Huxley (1851) and by Johannes Mailer (1858) in the calymma of radiolarians, were "undoubted cells," and also described later (1870) their structure and increase by division (3, p. 84), and But Cieu- showed that they constantly contained amyluin (4, § 90). 588 REPOliT OF COMMISSIONER OF FISH AND FISHERIES.

kowski first advanced the view tliat the yellow cells are iudepeudent unicellular organisms, parasitic algre, which for a time live in the bodies of the radiolariaus, but after tlie death of the latter come forth and multiply by division. This supposition was confirmed experiment-

ally by Karl Brandt (24, p. 05) and Patrick Greddes, who explained further the nature of their symbiosis, and finally showed the wide dis- tribution of the xanlliellece in the bodies of numerous marine animals, as well as their production of zoospores {ZoUxanthelht, PhilozoUn). Whether these are ontogenetically connected with certain "yellow unicellular algfe" which live free in the plankton, remains to be farther investigated. Perhaps also in this group belong the Xanthidea which

"were described by Hensen (9, p. 79) and Miibius (10, p. 124) as species of XantJiidium and as " spiny cystids,"' spherical cells which reach 1 millimeter in diameter, contain yellow diatomin granules, and multiply by division. Their thick hyaline shell, which seems to consist of slightly silicified cellulose, armed with simple or star-shaped radial spines, is characteristic. I find these Xanthidea' very numerous in the oceanic plankton. Perhaps the siliceous-shelled Xanthidia, which Ehrenberg has found so abundantly as fossils, also belong here. 6. Bictyoeheie.—The ornamented latticed cases of the Dit'tyochida', formed of hollow siliceous spicules, are often found in great numbers in the plankton, pelagic as well as zonary. Although these have long- been known, both living and as fossils, to microscopists, two very dif- ferent views as to their true nature are entertained.* In a preliminary contribution " On the Structure oi Dlstephanus [Die- iyocha) speculum''' Zool. Anzeiger, No. 334, one of my earlier students, Adolf Borgert, briefly showed that each single case contains an inde- pendent ciliated cell. He therefore considered it a new group of Flageh lata (or MastUjophora), for which he proposed the term SiUcoJiaiieUata.

The "twin parts" described by me (4, p. 1549) lie regarded as a double case which had arisen through the conjugation of two individual jiayellaia. To my mind this new interpretation seems to have very considerable probability, although I do not regard it as settled that the ciliated cells are the swarm-spores of the Pluvodarium. In case

* Ehrenberg, who in 1838 and 1841 first described the oruaiueuted siliceous skele- tons of Dictyocha and Mesocena, called them diatoms and distiugnished no less than 50 species of them, some living, some fossil. Later, at Messina (1859), I noticed, inclosed within the ornamented hat-shaped latticed shell a small cell, and on that account referred it to the Radiolaria, with reference particularly to the similar siliceous skeletons of some XasseUaria ( Acan thodesm ida). Twenty years later E. Hert- wig found a spherical Pha'adarium, the surface of whose calymma was covered with numerous Dictyocha little hats (Dictyocha-Hutchen), and he therefore believed that they must belong to this legion. He compares the single siliceous little hats Hutchen) with scattered ( the spicules of the Spha'rozoida. In my ChaUenyer report (4, p. 1558) I agreed with this interpretation; so much the more when I myself saw nu- merous similar Fhwcystina (Dictyocha stapedia) living among a similar I'ha'odaria in Ceylon, and found specimens in several bottles of the ChaUenyer collections, espe- cially Station from 144, from the Cape of Good Hope (4, p. 1561, pi. 101, Figs. 10-12). PLANKTONIC STUDIES. 689 the greenish-yellow pigment granules in the protoplasm of the Die- tyochida' are chlorophyll or phytochrom, they must be placed with "unicellular alga^." If, as I believe, the supposition of Borgert is cor- rect, then the masses of DictyocUdw shells found so abundantly in the calymma of Ph(codaricv can be regarded only as the empty shells of Silicqfiafiellata, which the skeletonlessP//ft'o^7/?ia has taken in as food. This supposition is much more probable since these, together with sili- ceous scales of diatoms and tintinnoids,have been found in great num- bers in the calymma of other radiolarians. This case would then be analogous to two similar appearances which I myself have previously described, My.vobrachia pliiteiis (4, p. 22) and Dalcaromma calcarea (4, p. 70, § 102). 7. Peridinece {Dinoflaficllata or Binoeytea, earlier Gdioflagellafa).— This group of Flagellata (or Masfifjophora) earlier placed with the In- fusoria, has lately, with more certainty, been recognized as a proto- phytic group with vegetable metabolism. They are represented in the plankton by numerous and, in part, remarkable and beautiful forms, a part of which have been lately figured by Stein under the name Arthrodele flagellata. Many such forms occur in the neritic, fewer in the oceanic plankton, and often in such masses that they take a great part in the formation of the fundamental food supply. Henseu cor- rectly points out the great importance of these Frotista, of whose quantity he attempted to give a conception by counting (9, p. 73). Many of these participate in a prominent way in the marine popula- tion (Ce>v^^^^m, Prorocentrum, etc.). John Murray very often found chains of Ceratmm tripuH (each composed of eight cells) floating in the plankton of the open ocean, without ciliary movements, while the ciliated single cells inhalnted the neritic plankton in vast numbers close to the shore. Sometimes these crowds of Peridinew, like the diatoms, appeared so abundantly as to till the tow net with a yellow slime (G, p. 934).

I?. —METArUYTES OF THE PlANKTOX.

The only class of metaphytes which occurs in the plankton are the alga^. The great majority of this class, so rich in forms, belong to the littoral benthos; only a few forms have adopted the pelagic mode of life, and of these only two, from their great abundance, are of any considerable importance in the oceanic fundamental food supply, the Oscillatorkc which live in the depths, and the /Sarfiassa which grow at the surface. A third group, the Halosphwrea', is much less abundant and important, but of considerable interest in many relations.*

*The OscUlalorkv must be regarded as true algi«, since their characteristic "jointed threads" {" Glicdcr-faden") form an actual ThaUm^. and indeed a thread-like thallus, the Volvo- as iu the Conferva-. But on the same grounds also we must regard as algw also multicellular Meiaphytts, cinea and Halosplurrew with spherical thallus ; they are which show the simplest form of tissue (Hhfone.9, 30, p. 420). The foregoing proto- is only a simple types, on the other hand, have no tissue, since the entire organism cell (Protista, 30, p. 453), 590 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

1. HaJospha'recv.—Under the name Halosplucra ririilis, Schmitz (187(() first described a new genus of green algse from the Mediter- ranean, which appear floating in the plankton of the Gulf of Naples in great numbers from the middle of January until the middle of April. They form swimming hollow spheres, from 0.5.") to 0.62 mm. in diameter, whose thin cellulose wall is covered within by a single layer of chloro- phyll containing cells analogous to- the blastoderm of the metazoic egg. Each of tbese epithelial cells divides later into several daughter cells, each of which forms four cone-shaped swarm-spores with two ciliated cells. I have known this green ball for thirty years. In Feb- ruary, 1800, I found them numerous in the plankton of Messina. I observed a second kind in February, 1807, at Lanzarote, in the Canary Islands. The hollow spheres found in the Atlantic are twice as large, and reach a diameter of 1 to 1.2 mm. They have pear-shaped swarm- spores. I named them Rcdospha-m blastida. Morphologically these hollow spherical algfe are of great interest, since they are directly com- parable to the blastula (or blastosphere stage) of the metazoic embryo. As the latter is to be regarded as the simplest type of the metazoon, so Halosphcera (like Volvox) can be looked upon as the primitive ancestral form of the Metaphyta (4, p. 499). Hensen has lately found numerous living specimens of i7a?os/)//ft'ro r/m7/.y in five hauls from a depth of 1,000 to 2,000 meters (10, p. 521). The light of the bathybic luminifer- ous animals may possibly be sufficient for their metabolic activity. 2. Oscillator'uv.—Like the diatoms in the cold regions of the ocean, the oscillatoria? THcliodesmium its ( and allies) are found in the warm regions in inconceivable quantities. It is very certain that the latter, as well as the former, belong to the most important source of the " fundamental food supply." Ehrenberg in 1823 observed in the Ked Sea, at Tur, such large quantities of Trichodesmium erytlircenm that the water along the shore was colored blood-red by them. Mobius has re- cently carefully described the same thing anew, and has (quite cor- rectly) traced from it the name of the Eed Sea (26, p. 7). Later, I myself found just as great numbers as these in the Indian Ocean at Maledira and Ceylon (25, p. 225). In Rabbe's collections are several bottles of plankton (from the Indian and Pacific oceans) entirely filled with them.* The Challemjer fo\m(\. great quantities of Trichodesmmminthe

Arafura Sea and Celebes Sea (0, p. 545, 007), and also in the Guinea stream (0, p. 218) ; and between St. Thomas and the Bermudas (6, p. 130) wide stretches of the sea were colored by it dark red or yellowish brown. Murray found it only in the superficial, never in the deeper layers of tbe ocean. 3. Sargasse(e.—The higher algfe are represented in the planktonic flora only by a single group, the Sarcjassece, and these again are com-

*In the collection of Eadiolana, which may he purchiised from the famulus Franz Pohle, at Jena, prejiaration No. 5, from Madagascar, contains many flakes of this 08ciUato)-ia. PLANKTONIC STUDIES. 591

Dionly only of a siiiiiie .species, iSaygassHm hacciferitm; but tliis lias the greatest iiiiportauce, since, as is known, it alone forms the lioating sargasso banks, which, cover such extensive portions of the ocean. Be- sides this very important species, other fucoids are found floating- in the ocean, especially species of Fucus {F. vesicnIosii.

The two great chief groui)s of unicellular animals, Rhizopoda and Infusoria, occur m the ocean in very difterent proportions, in the reverse condition to that in fresh water. The Infusoria {Flagellata and Giliata), which chiefly form the pro- tozoic fauna in the latter, are indeed represented in tlie sea by a great number of species, but the most belong to the littoral benthos, and only a few swimming species occur in such quantities that they are of importance in the plankton, the N'oetilucidw among the Flagellata, the Tintinnoida' among the Ciliata. Much greater is the wealth of the ocean in Ehizopoda, calcareous-shelled Thalamophora and siliceous- shelled JRaf?^o/

in the oceanic only where the coast water flows in (0, pp. 679, 750, 933). The common XoctUuea miUaris aud some rehited species sometimes cover the surface of the coast waters in such masses as to form a tliick reddish-yellow slime, often like "tomato soup," and at night are Tintinnus, Dictyocysta^ CodoneUa) brightly luminous. The Tintinnoidw ( appear in smaller quantities, but often in great numbers. Some forms of these elegant Ciliata are oceanic. Tlialamophora {Foraminifera).—The Thalanio2)hora, often and very properly called Foraminifera, were once generally regarded as ben- thonic. Xew observations first showed that a part of these are plank- tonic, and through the comprehensive series of observations by the ChaUemjer the abundant occurrence of these pelagic Foraminifera and their great part in the formation of that most important sediment, the Olohigerina ooze, was first established. All these Thalamophora of the plankton belong to the peculiar perforated Polythalamia, to the family of the Globiyerinidw; only OrhitHna (provided it is independent) to the Monoihalamia. The number of their genera (8-10) and species (20-25)

is relatively small, but the number of individuals is inconceivably great. By far the most important and numerous belong to the genera Glohifierina, Orhulina, and Fulvimdina; after these Splucroidina and Pullenia. They occur everywhere in the open ocean in nnmberless myriads. J. Murray could often from a boat scoop up thick masses of them with a glass, and never fished with the tow net in 200 fathoms

without obtaining some (5, p. 534). A few forms {Hastigerina and Cymhalopora) show more local increase in numbers, while others are rare everywhere {ChilostomeUa, Candeina). In the equatorial counter- currents of the Western Pacific, between the equator and the Caroline Islands, the Challenger fonnd "great banks of pelagic foraminifera. On one day an unheard-of quantity of Pulvinulina was taken in the tow nets; on the following day they were entirely absent, and Ful- lenia was extraordinarily abundant." These important observations by Murray I can confirm from my own experience in the Atlantic and

Indian oceans* (comp. 3, pp. 160, 188).

*The important relations of these pelagic Polythalamia to the rest of the fauna of the phmktou on the one side, as well as its importance in the formation of the "Globi-

gerina ooze" on the other, has been expressly stated by Murray (6, j). 919). I agree completely with him in the view that these oceanic (ilobit/crinidfc are true pelagic; rhizopods, which in part are found swimming only at the surface or at slight depths (autopelagic), in part at zones of dilferent depths (zonary), hut they are not ben- thonic. The enormous sediment of "Glohigerina ooze" is composed of the sunken calcareous shells of the dead pelagic animals. On the other hand, the benthonic thalamophorcs, living partly abyssal, on the bottom of the deep sea, partly littoral, creeping among the forests of seaweed on the coasts, are of other sj^ecies and genera. They develop a much greater variety of ibrin. The neritic thalamophorcs found swimming in the coast waters are in part .again characterized l)y various forms. PLANKTONIC STUDIES. 593

Badiolaria.—Ti^o class of organisms has remained so long uiiknowu to us, and by the brilliant discoveries of the last decade has been sud- denly placed in so clear a light, as the Radiolarla (comp. 4, § 251-2G0), For half a century we knew next to nothing of these wonderful rhizo- pods; to-day they appear as one of the most important planktonic classes.* These, the most varied in form of all the unicellular organ- isms, forni a purely oceanic class, and live and swim in all seas, especially in the warmer ones. ^N'umenms species are also found near the coasts, yet these are not distinguishable from those of the open sea. They constitute no separate neritic fauna.

'S-'ast crowds of Radiolaria occur at the surface of the ocean, as well as at different depths. Long ago Johannes Midler remarked:

It is a great plieuomeuon that Araiithomeira can be takeu daily by tlionsaiids in a calm se.1 and independently of storms; and tiiat of many specits of rolycijatina, hnndrcds of individnals were seen during my last residence at the seashore (2, p. 25).

I have tried myself, on the hundreds of voyages to different coasts which I have made since 185(5, to thoroughly study the natural history of the Radiolaria. The incomparable collections of the Challeru/er afforded me by far the richest material for observation. The results obtained therefrom are embodied in the report (18S7). Among other references to the conditions of the plankton there mentioned, it brought up the following pro])ositions: (1) Badiolaria occur abundantly in all seas which contain a medium amount of salt, and which do not (like the Baltic) receive a sti'ong influx of fresh water. (2) In the colder seas only a few species occur (chiefly Acantharia), but immense quan- tities of individuals; towards the equator the variety in form gradu- ally increases (horizontal distribution, comp. 4, § 220-2.31). (3) The chief groups of Radiohtria are distributed unequally in the five bathy- zones or girdles of depth of the open ocean. The subclass Porulosa (the two legions of S^nmellaria and Acantharia) inhabit especially the two upper zones. On the other hand, the subclass Oscidosa {Nasselaria

*After Ehreuberg, in 1847, had described the siliceous shells of some hundred species from the Barbados, we obtained in 1858 the first description of their organ- ization through Johannes Miiller. In the Avork with which this great master closed his renowned life he described 50 species which he had observed alive in the Med- iterranean Sea (2). ^Vhen in continuation of this I devoted a winter's residence in Messina to their i'urther investigation, I was able in 1862, in the monograph con- aesiuent thereupon, to distinguish 144 new species, in all 113 genera and 15 families (3). But this rich Badiolaria fauna of Messina still gave no promise of the immense quan- tities of these delicately ornamented creatures peopling the open ocean, and whose variously formed siliceous shells, sinking to the l)ottom after death, formed that wonderful sediment, the "Badiolaria ooze." This was fust discovered thirteen years later by the Challenger. The investigation of the fabulous radiolariau treas- ures (chiefly from the Pacific) which this expedition brought home has led to the discrimination of 20 orders, 85 families, 739 genera, and 4,318 species (4, v) 256). Further study of the Badiolaria slime of the deep sea will bring to light many new forms from this inexhaustibly rich mine. H. Mis. 113 38 594 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

and Phccodaria) move in tlie three loAver zones (vertical distribution,

4, § 232-239). Tlie dependence of their appearance upon the various conditions of life has been investigated by Brandt (24, p. 102).

D. —('(ELENTEKATES OF THE Pl.AXKTOX.

The ancestral group of the coelenterates has important significance

and manifold interest for the natural history of the plankton j still this applies in very varied degrees to the different principal groups of this numerous circle (comp. 30, p. 522). The great class of the spojiges, which belongs exclusively to the benthos, has never acquired a ])elagic habit of life. The phylum of the 2)latodes also needs no further reference here. We know, to be sure, a small number of pelagic turbellarians and trematodes. Arnold Lang, in his monograph on the sea-phiuarians

or polyclads (1884, j). G29), mentions as "purely pelagic" or oceanic 8 species and 4 genera [Flanocera, Stylochns, Leptoplana, Planaria). Parasitic trematodes are occasionally found as "pelagic parasites" in medusiie, siphonophores, and ctenophores; but these trematodes and

turbellarians are usually found only individually ; they never appear in such quantities as are characteristic of the majority of the plankton animals. Much more important for us is the third type of the coelen- terates, the diversitied chief group of the nettle animals or Cnidaria

(30, p. 524). Cnidaria.—With reference to the mode of life and the form condi- tioned thereby, one may divide the whole group of Cnidaria into two great principal divisions, polyps and acalephs, which since the time of Cuvier have lain at the foundation of the older systems. The polyps (in the sense of the older zoiilogists) eral)race all nettle animals, Avhich are fixed to the bottom of the sea, hydropolyps as well as scyphopolyps (Anthozoa). They belong exclusively to the benthos. Only a few forms have acquired the pelagic mode of life {Minyadoe^ Arachanactis, iarvte of Actinioe, Cerinthidce, and some otlier corals). The second principal division of the nettle animals, the Acalcpha, embraces, in the sense of their first investigator Esclischoltz (1829), the three classes of meduste, siphonophores, and ctenophores; all swimming marine animals, which, from their richness in forms, their general distribution in the ocean, and their abundant occurrence, possess much importance for plankton study. Since the above-mentioned pelagic polyps {Minyadce, etc.) on the whole are rare, and never appear in great quantities, we need make no further reference to them here. Much more important are the Aca- lejyJis, which offer a fund of interesting problems for plankton study. Commonly, all these animals are roughly termed "pelagic," but a new consideration shows us that they are so in a very different sense, and that the distinction which we have made above in reference to their chorological terminology here finds its complete Justification. We Avill first consider the medusae, then the siphonophores and ctenophores. PLANKTONIC STUDIES. 595

Me(Jusa\—Tlie great interest wliicb I have felt in this wonderful class of animals sin<'e my first acquaintance with living medusjc, in 1854, and which has been increased by my nunierous sea voyages, led me to the monographing of them (1879). I immediately gained thereby a number of definite chorological and (Ecological ideas, which have been of permanent influence in the further course of my plankton studies. By it was definitely fixed the knowledge that the wliole race of the medusie is polijphi/Jctic, and that on the one side the GraHpcdoia (or Ili/dromedusa') have arisen independently from the Hyclropolyps, just as (^n the other side the Aeraspedota (or Scypliomcdnsw) from the kSeyplio- poJyps. In both analogous cases the transition to the pelagic, free- swimming mode of life has led to the formation, from a. lower, sessile, very simply organized benthic animal, of a much higher plauktonic meta- zociu, with differentiated tissues and organs—a fact which is of great significance for our general understanding of tlie jjliylogeny of tissues. I have in that monograph broadly distinguished two principal forms of ontogeny or individual developmental history among the medusae, metagenesis and hypogenests. Of these I regard metagenesis, the alter- nation of generations with polyps, as the primary o\ paUngenetlc form; on the other hand, hypogenesis, the "direct develoiDment " without alter- nation of generations, as the secondary abbreviated or cenogcneUc form. This distinction is of great importance in the chorology, in so far as the great majority of the oceanic medusjc are hypogenetic; the nentic, on the other hand, are metagenic. To the oceanic medusae in the widest sense I refer the TracJiylinw {Trachymedusw jyid Narcomedusa') among the (Jraspedota; to the neritic, the Leptolincc {Anthomedusw and Leptome- dusev: comp. 29, p. 233). While the former have lost their relation to the benthonic polyps, the latter have retained it through heredity. The same seems to obtain also for the majority of the Aeraspedota, namely the JHseomedusa\ Among these there are only a few oceanic genera with hypogenesis, e. g., Pelagia. The development of the smaller but very important acraspedote orders, which I have distinguished as ISfau- romedusa\ Peromeditsa^, and Cuhomedusw, is, I am sorry to say, as yet quite unknown. The first is to be regarded as neritic and metagenic; the two latter, on the other hand, oceanic and hypogenic. That the majority of the large Disconiedusce are neritic and not oceanic is shown from their limited local distribution. Although ten years ago the Medusw were generally held to be purely pelagic animals, it has now been found that a certain (j^erhaps consid- erable) part of them are zonary or bathybic. Among the 18 deep-sea medusce which I have described in part xii of the Challenger Eeport (1881) there are, however, some forms which occur also at the sur- face, and a few which perhaps were accidentally taken in the tow net while drawing it up. But others are certainly true deep-sea dwellers, as the Pectyllidev among the Oraspedota, the PeriphylUdw and AioUidw 596 REPORT OF COMMISSIONER OF FISK AND FISHERIES. amongj tbe Acraspedota. Some Meduscc have j^artly or entirely given up tbe swimming- mode of life, as Polyclonia^ Cephea, aud other Rhiz- osfo))ia, which lie with the back towards the sea bottom, the iiiany- mouthed bunch of tentacles directed upwards. The Lucernaridw have completely passed over to the benthos. Mnny.l/ert^sft' are spauipelagic, rise to the surface only during a few mouths (for the purpose of reproduc- tion!), and pass the greater part of the year in the depths; thus in the Mediterranean the beautiful Cotylorrhiza tuberenlata, Chdryhdea marsu- pialis, Timajfavilabris, and OUndias miilleri. These bathybic forms are sometimes brought up in great numbers with the bottom net (19, p. 122). Many cling with their tentacles to Alr/fc and other objects (20, p. 341). The immense swarms in which the MednMv sometimes appear, millions crowded thickly together, are known to all seafaring naturalists. Tlius in Arctic waters, Codon'mm princcp^^^ Hippocrene superciliaris; in tlie North Sea, Tiara pilcata, Aglantha digitalis; in the Mediterraiieau, Liriantha mncronata, Rliopalonema velatum; in the tro^ncs, Cytms nigritina; in the Antarctic Ocean, Ilippocrene mocloriana and others.

Hensen (9, p. 05) in the North Sea found a swarm of Aglantha^ the number of which he estimated at twenty-three and one-half billions. The extent of the multitude was so great that "the thought of approxi- mately estimating the animals in this swarm must be given r.p." In such cases the whole sea for a few days, or even weeks, seems every- where full of Mediisw; and then again weeks, or even months, may jiass without finding an individual. The uncertainty of appearance, the " capriciousness of these brilliant beauties," in other words the depend- ence upon many different, ancl for the most part unknown causes, is in this interesting animal group remarkably impressed upon us. I will, therefore, in another place, referto it orithe ground of my own experience. Siphonophorcs.—What I have said above concerning the unequal dis- tribution of the medusa? applies also to their wonderful descendants, the purely oceanic class of the siphonophores. This highly interest- ing class was, up to a few years ago, also regarded as purely jjelagic; but of these, too, it is now known that they are in great part bathy- pelagic, in part also zonary and bathybic. The new and very peculiar groui^ of the Ai(ronecfa' {Steplialida' and BJuMlalida'), taken by the Chal- lenger at a depth of 200 to 000 fathoms, is described in my '^ Report of the Siphonophores of H. M. S. CMllenger'^ (1888, p. 290). The Batky- phy.sa taken by Studer, and some of the Rliizopliysidw [Auropkysa^ Lino- pliy^a) captured by the Gazelle, were taken at a dej)th of 000 to 1,000 fathoms (1. c). But that such deep-sea siphonophores (probably mostly RhizopJiysida') inhabited the ocean in great masses was first shown by

Chierchia (8, p. 84-80). Previously, in numerous soundings which the Vettor Pisani had made in the Atlantic and Pacific oceans, the line of the deep-sea lead when drawn up was found to be wound around with the torn-off stinging tentacles of great sij)honophores. By means of —

PLANKTONIC STUDIES. b97 the new elosible net iji vented by Palumbo, be was enabled to bring up the entire animals from deliiiite deptlis. From these experiments Cbiercliia concluded ''that certain characteristic si)ecies of siphonophores live in great numbers at certain depths, from 1,000 meters above the bottom n]>wards, the strongest and most resistant in the depths, the vreaker higlier up" (8, p, 80), Other siphonophores, wliich belong to the forms most numerous at the surface, extend down to considerable depths, as

Diplujes sieholdii (15, p. 12). The larvai of Hippopodius luteus, which are very numerous in winter and spring, have quite disap])eared iii summer, and, according to Chun, live in greater deptlis, even to 1 ,200 meters (15, p. 14). Other forms are spanipelagic and come to the sur- face only for a short time, only a few weeks in the year, like so many Physonectw. From these and other grounds the participation of the sijDhonophores in the plankton, like tiiat of their ancestors, the Hydro- vieduscc, is extremely irregular, and their appearance at the surface of the sea is subject to the most remarkable changes. Ctenopliores. —This Cnidarian class also, like the preceding, is purely oceanic, not neritic. They also show the same phenomena of jielagic distribution as the i

E. Helminths of the Plankton.

The race of the helminths or "worms" (the cross of suffering for sys- tematic zoology) obtains a more natural unity and more logical defini- tion, if one removes therefrom the platodes and annelids, placing the former with the coeleuterates, the latter with the articulates. The jus- tice of this limitation and also the grounds for regarding the worms as the common ancestral group of the higlier animals, I have set forth already in the "Gastrea Theory" (1873), and many times at later op- portunities, last in the eighth edition of my "Natural History of Crea- tion" (1889, ]). 510). Tliere remain then as helminths, in the narrower sense, four divisions with about 12 classes, namely, (1) the Rotatoriw 598 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

{Trochospharn, lehthydina, Rotifera) the ^Strongt/ktriw ; (2) {Kenuttoda, Acanthocrpltala, Chwtognatha); (3) tlie Rhynvhocala {JVcmertina, En- teropneusta), and (4) the Prosopygkv {Bryozoa, BracMopoda, Phoronea\ Sijmnculea'). The larviB of iiiaiiy of tliese worms liave acquired the pehigic mode of life, but most of them are too small aud too scattered in the plauktou to be of any considerable imi)ortance in its composition. Chcctoynatha.—In its mature condition only a single class of hel- minths plays an independent and indeed an important role in the plank- ton—the small and peculiar class of arrow-worms or CJuctognatka {Sagitta, Spadella, etc.). These, together with the copepods, salpae, pteropods, and radiolarians belong to tlie most substantial, most gen- erally distributed, and usually unfailing constituents of the plankton.

Hensen (9, p. 59) has made some calculations of the immense numbers in which they ap})ear. He reckons them in the '^ perennial plankton," yet does not find " everywhere the regularity which one might expect." He is astonished at the " highly remarkable variations" in their num- bers, and finds this very unequal distribution very puzzling (9, p. 60). Chun has lately shown that the troops of ^Sagitta not only populate the surface of the sea, but also "in common with the liadiolaria, Tomop- teridce, Diphyidcv, Crustacea, constitute the most numerous and most constant inhabitants of the greater depths. In countless multitudes they are taken in the open as well as in the closible net, from 100 " meters down to 1,300 meters (15, j). 17). It seems that Sagitta, as a whole purely oceanic, is represen.ted by pelagic as well as zonary and bathybic species.

F. —MOLLUSKS OP THE Pl.ANKTON.

The race of mollusks play a very important role in the plankton. Although the great majority of the genera and species belong to the benthos, yet there are a few families which have become adapted to the pelagic mode of life, of great importance on account of the great swarms in which they often appear. The three chief classes which we distinguish in this race (30, p. r)4:()) live very differently. The Acepliala, entirely benthonic, can take part only as swarming larva? in the com- position of the plankton; so also the swimming larva? of many mero- planktonic Gastropoda. Of these latter only a very few genera have adopted completely the pelagic mode of life, like lanthina among the prosobranchs, GJavcns and PhyUirrlm among the opisthobranchs. Pteropods and Heterojmls.—These two grou])s of snails are holoplank- tonic, chielly nyctipelagic animals, which come to the surface of the sea, preferably during the night, in vast numbers (14, pp. 121-125). Chun has lately discovered that many of them are found at considerable depths (15, p. 3G). Some kinds of pteropods {e. g., Spirialis) seem to belong to the zonary and bathybic fauna. The heteropods are on the whole of less importance. They occur in great swarms less frequently and only in certain parts of the warmer seas. The pteropods on the PLANKTONIC STUDIES. 599 other hand surpass the former, not only by a great diversity of genera and species, but particularly from their enormous development in all parts of the ocean. Clio and Limacina are known to occur in the Arctic and Antarctic ocean in schools so vast as to form the chief food supply of the whales; the swarms of Creseis, Hyalea, and others which appear in the seas of the warmer a? id temperate zones, are also so con- siderable that these fluttering "sea butterflies {Farfalle di marey often play a very important part in the "cycle of matter in the sea" [StoffwecJisel des Meeres^^). The irregularity of the distribution and phenomena is also shown by the fact that Hensen, during his plankton expedition through the iSTorth Sea (July and August, 1887), completely missed the pteropods (9, p. 50; 10, p. 110). On the other hand, when in August, 1879, I fished at Scoury, on the northwest coast of Scotland, we found such immense quantities of Limacina (during the forenoon in still w^eatlier) that these pteropods certainly formed more than nine-tenths of the entire lilankton, and with a bucket we could scoop up many thousands. The mass of the swarm had the same density for a deptli of two fathoms and for more than a square kilometer in horizontal extent. Cephidopods.—Although entirely swimming animals, these highly developed mollusks for the most part do not fall under the term plankton, if with Hensen we limit this to those "animals floating involuntarily in the sea" (9, p. 1). They must then be included in the "uekton;" but naturally it depends in some cases entirely on the strength of the current whether the small cephalopods should be included in the former or in the latter. In any case this highest developed class of mollusks is of very great importance in the i)hysiology of the plankton, the question of the " cycle of matter in the sea." On the one hand they daily consume vast masses of pteropods, Crustacea, sagitta, medu- sa?, and other planktonic animals; on the other, they furnish the most important food for fishes and cetaceans. From recent investigations it is found that the cephalopods are j)artly pelagic, jiartly zonary or bathybic {Spirilla, ¥autilus, etc.). Characteristic small, transparent Deeolenie {LoUgopsidtc) are known as partly pelagic, partly bathybic species (15, p. 36). The same is true also of some Octolenw {Philonexidw). Young forms of cephalopods are captured swimming in the plankton at the surface as well as in the depths.

G. —ECIIIXODEKMS OF THE PLANKTON.

The rayed animals in their significance in the plankton, as also in many other morphological and physiological relations, show highly peculiar and varied conditions. Although all echinoderms are without exception i)urely marine animals, and no single form of this great group inhabits fresh water, still not a single species has completely adopted the planktonic life. Not a single echinoderm in its full-grown and sexually mature condition can be called pelagic. The few forms \y^hich temporarily swim about {Comatalida;} belong only to the neritic —

600 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

fauiui and do uot occur in the ocean. They also are found in such limited numbers that they are without importance for the plankton. Much more important for us are the free-swimming echinoderm larvas, which often ijlay a great part in the neritic plankton. Indeed they are classical objects in the history of plankton investigation; for to their study their disco v^erer, Johannes Miiller, forty-five years ago first ap- plied the method of "pelagic fishery with the fine net," which soon led to such remarkable and brilliant results. The distribution and number of the larval rayed animals is naturally dependent upon that of their benthonic parents; but in addition also partly upon chorological, partly oecological causes. According to Sir Wyville Thompson (14, ii, pp. 217-245; G, p. ,379), the remarkable metamorphosis, discovered and de- scribed in a masterly way by Miiller, is the rule only among the littoral

forms, chiefly in the temperate and warm zones; on the other hand, it is the exception in the case of the majority, for star animals of the deep sea and cold zones, in the Arctic as well as in the Antarctic, develop directly. Therefore, great troops of pelagic larvaj of these animals occur commonly oidy in the neritic jjlanlton of the temperate and warm zones, uot in the open ocean. They seem to visit the depths (below 100 meters) very seldom (15,. p. 17). Besides, their appearance is naturally connected with the time of year of this development; often oidy during a few months (9, p. 02). The variation in the constitution of the "periodic plankton" is here very remarkable.

H. Articulates of the Plankton.

Of the three chief divisions which we distinguish in the group of articulated animals (30, p. 570) two, the Annelids, and Traeheates, take no part in the constitution of the plankton. Both are represented only by a few pelagic genera, and these have a limited distribution. Much greater in importance is the third chief division, the Crustacea. It is the only animal class which is never lacking in the tow-net collections (or only very exceptionally), and which commonly appears in such numbers that their predominant position in the animal world of the sea is evident at the first glance. This applies as well to the oceanic as to the neritic fauna, to the littoral as to the abyssal benthos. Annelids.— Tha great mass of this group, so rich in forms, belongs to the benthos, is and represented in the abyssal as well as in the litt(u-al fauna by numerous creeping and sessile forms. Only very few ringed animals have acquired the pelagic mode of life and have assumed the characteristic hyaline condition of the oceanic glasslike animals, the swimming Tomopteridcc and Alciopidw. Both families are represented in the plankton only by a few genera and species, and as a rule their 'uimber of individuals is uot very considerable. Chun has lately shown by means of the closible net that both forms, Tomopteris as well as Alciopc, are rei)resented in the different depths, from 500 to 1,300 meters, by peculiar zonary and bathybic species, which are distinguishable PLANKTONIC STUDIES. 601

from the pelagic species of the surface by cliaracteristic marks. "The wealth iu such Alciopidw (and Tomopteridce) at all depths of 100 meters

or over is very surprising, and it requires a caveful scrutiny, for the beau- tiful trauspareut worms ofteu press actively by dozens in serpentine course through the crowd of other forms in the dishes'' (15, p. 24). Crustdcea.—In their general

yellowish or reddish "animal uiiish/' composed in by far the greater part of copepods. In the journal which I kept in the winter of 1S0G-G7, at Lanzarote, in the Canary Islands, of the varying constitution of the plankton, for " many days there is only the remark : almost pure buck- ets of copepods," or " the collection consisted almost entirely of Crus- tacea, by far the greater part of copei)ods." That these small crus- taceans form the chief food suj^ply for many of the most important food-fishes {e. g., the herring) has long been known. In the Arctic as well as the Antarctic Ocean Calanus finniarcMvus and a few related species form in general the chief bulk of the plankton, and furnish food for pteropods and cephalopods, for the divers and penguins, for many fishes and whales. On the voyage from Japan to Honolulu the ChaUemjer sailed through wide stretches of the :N"orth Pacific Ocean which were covered with red and white patches, caused by great accumulations of two species of small copepods, the red being Calanus propinquus (8, p. 758). In many other regions, from the Polar Circle to the Equator, the ship passed through white bauds many miles wide, composed solely of copepods (8, p. 843). That their appearance is very irregular and dependent on many conditions is true of this very important group of plankton animals as for all others. For two days the Challenger went through thick shoals of Corycaeus pellucidus. For the next three days the copepods had entirely disappeared. Hensen has made statistical statements upon the appearance of the copepods of the Xorth and Baltic seas (9, p. 45). Chun has lately showu that this order plays a highly significant role, not only at the surface, but also at considerable depth? (000 to 1,300 meters), (15, p. 25). " Their abundance and richness in forms in greater depths is absolutely aston- ishing. Larval forms of species sessile or living upon the bottom min- gle in confusion with the young forms and sexually mature stages of enpelagic species. Many species hitherto regarded as varieties are numerously represented in the depths." On the other hand, the order seems to be very poorly represented at very great depths. The Chal- lenger found only one very characteristic deep-sea species in 2,200 H'diliom^—PontostratioUles ahyssicolla .{S, p. 845). Some genera never leave the surface and are autopelagic, e.g., Pontellina (15, p. 27). Ostracoda.—ThQ ostracods are, next to the copepods, the most impor- tant Crustacea of the plankton, and are represented at the surface as well as in ditterent depths by masses of many species. In the (ecology of the ocean they play a similar role, as do the near-related cladocerans {I)aj)hni(hv) in the fresh water. The Challenger collected 221 species of ostracods. Of these 52 were found below 500 fathoms, 19 below 1,5(>0, and below 8 2,000 fathoms in depth. Many ostracods, like many cope- pods and other crustaceans, belong to the most important luminous animals of the ocean. On my journey to Ceylon (in the beginning of November, as well 1881), as on the return trip (middle of March, 1882), I admired as never l)ef()re the oceanic light in its splendor. "The whole ocean, so far as the eye could reach, was a continuous shimmering sea PLANKTONIC STUDIES. 603 of light.'' Microscopical investigation of tho water showed that the luminous animals were for the most part small Crustacea {Ostracoda), to a less extent Medusa', Salpw, worms," etc. (25, pp. 42, 372). Chierchia, three years later, in the same region and in the same mouth, saw the same brilliant pheuomeuou: "The most brilliant emerald-green light was produced by an infinitude of ostracods*' (S, p, 108). Schizopoda.—Not less important in the planktonic life than the ostra- cods (sometimes even more important) are the schizopods. They also occur in wide stretches in immense swarms at the surface, as well as in greater and lesser depths. They also play a great role in the cycle of matter in the sea {Stoffa^echsel des Meeres); on the one side since tiiey devour great quantities of i^rotozoa and i)lanktonic larv;e, and on the other because they serve as food for the cephalopods and fishes. Many schizopods, like many ostracods and copepods, belong to the most bril- liantly luminous animals, and, like the latter, furnish very interesting problems for the bathygraphy of the plankton. G. O. Sars, w^ho has worked up the rich material collected by the (Jhallen(/er, di.stinguished 57 species, and found that 32 of these lived only at the surface, G from 32 to 300 fathoms, and 4 extended down below 2,000 fathoms (as far as 2,740 fathoms), (G, p. 730), Chnn also has discovered in the Mediterranean a number of new zonary and bathybic schizopods very different from the

pelagic varieties of the surface, Sfylochiron, A rachHomysis, etc. (15, p. 30). The phyllopods {Daphnida'), the amphipods {Phronimidw, Hyperi- dw), and the decapods {Miersida', Sergestidw) are indeed represented in the plankton by a number of interesting forms, partly oceanic, l^artly neritic; and some of these occasionally appear in considerable quantities. But as a whole they are of fjir less importance than the copepods, ostracods, and schizopods. The same applies also to the other groups of Crustacea, although many of them in their larval state take a great part in the constitution of the plankton. Also in regard to these multiformed and often nhujidaiit jjelagic crustacean larva', us well as for the mature crustacean animals, the advancing plankton study has still to establish and explain a fund of facts; namely, in relation to their pelagic, zonary, and bathybic distribution; their migra- tions, and the relations in which this planktonic fauna stands to the benthic fauna. Iiisecta.—That im^jortant branch the Tracheata, the most numerous in forms of all the principal divisions of the animal kingdom, has in the sea no representatives whatever. The Protracheata, Myriapoda, and Arachnidf ai-e exclusively inhabitants of the land and in small part of the fresh water, except the pycnogonids or pantopods (in case these really belong to the Arachnida'). Among the Tnsecfa there is only a single small group of true marine animals, tho family of the Halobatida'. These small insects, belonging to the Hemiptera, have completely ac- (piired a ])elagic mode of life, and run about in the tropical ocean just as our "water-runner" (Hydrometra) on the surface of fresh water. 604 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

Botli of the genera beloDging tliei-e {Ilalohates and Htdohdtodcs, witli about a clozea species) are limited to the tropical aud subtropical zoue. The Challenger fouud them iu the Atlantic between 35'^ north latitude aud 20^ south latitvule; iu the Pacific between 37'^ north latitude aud 23° south latitude. I myself observed Halobates numerously in the Indian Ocean, and on one day iu crowds in the neighborhood of Belli- gam. Although they can dive, they never go into the depths.

J. TUXICATKS OF THK PLAXKTOX.

The tribe of mantle animals falls into two chief divisions, according to their mode of life. The ascidlans belong to the heuthos; all other tunieates to the plankton. Tlie (Jopelata (or Appendicular l(la')'dve mor- phologically the oldest branch of the stem, and are to be regarded as the nearest of the now living relatives of the FrocJiordiniw, the hyr»o- thetical common ancestor of the tunieates and vertebrates (30, p. ()0."i). The near relationshi]) of the Gopelata and the ascidiau larva makes it very probable that the whole class of ascidians has sprung from the primarily i>elagic (Jopelata^ and has diverged from this through the acquirement of a sessile mode of life. The Liicidue or Pyrosomidce, on the other hand, are probably secondarily j)elagic animals, and sprang from the (Jwlocorniida', a benthouic synascidiau g'roup. The Thalidke (the DolioUdic as well as the Salpid(v) are to be regarded as primarily pelagic animals. These conditions are doubly interesting, because the tunieates in an exemplary manner demonstrate the peculiarities which the transition on one side to a sessile mode of life iu the benthos (in case of the ascidians), and on the other to a free-swimming mode of life in the plankton (in the case of all other tunieates), has bronght about. All the latter are trans[)arent and luminous fragile animals, poor iu genera and species, bat rich in numbers of individuals. The ascidians, on the other hand, fastened to the bottom, in part littoral on the coast, in part abyssal in the deep sea, are much richer in genera aud si^ecies, iu many ways adapted to the nmnifold local conditions of the bottom, and mostly opaque. The few hyaline forms {e.

no other forms of swimming liaiid we know of no neritic tunicates, omni- mantled animals which are found only on the coasts, except the present ascidian larva. planktonic Lately Chun has established the interesting fact tliat the in slight depths, tunicates occur in luimbers not only at the surface and into greater depths pp. but also during the summer extend down (15, the iMediterrauean new CopeJata, 32, 42). He discovered further in to the surface and wl'iich are only /onary or bathybic, never coming in size characterized by peculiar organization as well as difference [Megalocerens abyssorim, 3 centimeters long, 15, p. 40). small size, are The small, delicate Copelata and Dolioln, from their 8alp(c and naturally more difficult to see than the large luminous quantities of oceanic Pijrosoma. Whoever lias carefully examined great almost every- plankton can readily testify that the former also occur where and occasionally take an important part in the constitution of for example the the mixed plankton. Among the Salpcc there are From the smaller species which form extensive swimming shoals. the »aipas three-year observations of Schmidtlein it is learned tliat throughout the belong to the perennial plankton and are numerous wholeyear (19, p. 123).

K.—Vertehhates of the Plankton. most The vertebrates of the sea are in their mature condition for the to be part too large and have too powerful voluntary movements "animals carried reckoned in the true plankton in Hensen's sense, as aquatic involuntarily with the water." The sea fishes, as well as the easi-ly the impetus birds and mammals of the sea, overcome more or less by voluntary of the currents, and thereby prove their independence floating inver- movements, which is not commonly the case with the already shown tebrate animals of the plankton. Meanwhile I have is very above that this limitation of the i)/fmA-fo/i against the neJdon of the latter arbitrary and at any moment may be changed in fiivor through diminution of the strength of the current. For the chief point of the "cycle of of Hensen's plankton investigation, for the question importance, since matter in the sea," the vertebrates are of greatest daily consume the they, the largest of the rapacious animals of the sea, or indirectly. greatest quantity of plankton, no matter whether directly consume hundreds of A single sea fish of medium size may daily pteropods and thousands of Crustacea, and in case of the giant cetaceans fold. In a compre- this (pnintity may be increased ten or a hundred hensive consideration of the plankton conditions, and particularly in discussion, a thorough its physiological, ecological, and chorologieal investigation of the vertebrates swimming in the sea, the marine fishes, the aquatic birds, seals, and cetaceans, is not to be undertaken. We the pur- can then turn from it here, since it has no further relation to sense pose of this plankton study. We can here in Hensen's (9, p. 1) 606 REPORT OF COMMISSIONER OF FI^^H AND FISHERIES.

provisionally limit ourselves to the vertebrates of the sea "carried involuntarily witli the water," and as such (apart from a few small pelnjiic fishes) only the pelagic eggs, young brood, and larvte of the marine fishes come into consideration. Some few teleosts {Scojyelidce Trichiuridw, ct aJ.) occur sometimes in schools in the plankton and are partly autopelagic, partly bathypelagic. The remarkable Lejyto- cephaUchv are possibly planktonic larviie (of J\Inr(vnoid(v), which never become sexually mature (7, p. 502). Fish cf/f/.s. —The planktonic fish eggs, found in great numbers at the surface of the sea, as well as the young fish escaped from them, play without doubt a great role in the natural history of the sea. Hensen, whose planktonic investigation started from this point, had thereupon "based the hope to obtain a far more definite conclusion upon the supply of certain species of fishes than had hitherto seemed to be possible" (9 p. 39). But the assumption from which he starts is wholly untenable. Hensen says {loc. eit.):

It i8 scarcely to be doubted that an opinion upon the relative wealth of various kinds fish of in the Baltic or in any other part of theocean whatever can be obtained through the determination of the quantity of eggs in the area under consideration. Brandt also characterizes this proposition as very lucid and weighty (23, p. 517). This standard proposition of Hensen and Brandt, from which a series of very important and complicated computations are to be made, was disposed of in a brilliant manner thirty years ago by Charles Darwin. In the third chapter of his epoch-making "Origin of Species," treating of the "Struggle for Existence," Darwin, under the head of Malthus' theory of population, speaks of the conditions and results of individual increase, the geometric relation of their increase, and the nature of the hindrances to increase. He points out that "«? aU cases the average number of individuals of any species of plant or animal depends only indirectly on the number of seeds or eggs, but directly on the conditions of existence under which they develop." Striking examples of these facts are every Avhere at hand, and I myself have mentioned a number of them in my "Natural History of Creation" (30, j). 143). Still, to draw a few examples from the life of the plankton, I recall in this connection many pelagic animals c. ; g., Crustacea and medusae. Many small medu- sae, which belong to the most numerous animals of the pelagic fauna {e. g., Obelia and Lirope) produce relatively few eggsj as also copepods, the conmionest of all planktonic animals. Incomparably greater is the number of eggs produced by a single large medusa or decapod, which belongs to the rarer species. So, from the number of i)elagic fish eggs not the slif/htest eonelusion can be drawn as to the number of fish which develop from them and reach maturity. The major portion of the planktonic fish eggs and young are early consumed as food by other animals. PLANKTO:VIC STUDIES, 607

v.—COMPOSITION OF THE PLANKTON.

The composition of the planlcton is in quccUtative as well as quantitative relations very irregular, and the distribution of the same in place and time in. the ocean also very unequal. These two axioms ap^ily to the oceanic as well as to the neritic plankton. In both these important axioms, which in my opinion must form the starting-point anil the foundation for the cecology and chorology of the plankton , are embodied the concordant fundamental conceptions of all those naturalists who have hitherto studied carefully for a long time the natural history of the pelagic fauna and flora. The surprise was general when Prof. Ilensen this year advanced an entirely oi>posite oj)inion, " that in the ocean the plankton was dis- tributed so equally that from a few hauls a correct estimate could be made of the condition in a very much greater area of the sea" (22, p. 243). He says himself that the plankton exi)edition of Kiel, directed by him, started on this ''• purely theoretical view^'' and that it had '-'full results because this hypothesis was proven far more completely than could have been hoped" (22, p. 24t).* These highly remarkable opinions of Hensen, contradictory to all previous conceptions, demand the most thorough investigation; for if they are true, tlien all naturalists who many years previously, and in the most extensive compass, have studied the composition and distri- bution of the plankton are completely in error and have arrived at entirely false cx)nclusions. If, on the other hand, these propositions of Plensen are false, then his entire plankton theory based thereon falls, and all his painstaking computations (on which in the last six years he has spent 17,000 hours, which he wishes to have number the individ- uals distributed in the plaidvton) are utterly worthless. In the first place, the empirical basis upon which Hensen founded his assumptions must be proved, " starting from a purely theoretical point of view. " The plankton expedition of Kiel was 9.'> days at sea, and in the months of late summer (July 15 to November 7) which, as is known, offer m the northern hemisphere the most unfavorable time of all for pelagic fishery (28, p. 1(3, 18). Hensen himself says that it bore the "character of a trial trip" (22, p. 10), and his companion Brandt names it a "reconnaissance " upon which they had come to investigate rapidly

^ Heusen speaks of this in the following terms: "Hitherto it was the prevailing A'iew that the inhabitants of the sea were distributed in schools, and that one, ac- cordiug to luck and chance, according to wind, current, and season,' sometimes came upon thick masses, sometimes upon uninhabited parts. Tliis in fact applies only in a certain degree ior the harbors. For the open sea our knowledge teaches that nor- mally regular distribution obtainstliere, which changes in thickness and ingredients only withiu wide zones corresponding to the climatic conditions. I7i any case one must seek the variation from su<;h condition according to the cause which has pro- duced it, aud the occurrence of iueiinality is not to be taken as the given starting- point for relative investigation" (22, p. 244). 608 REPORT OF COMMISSIONER OF FISH AND FISHERIES. in succession as great areas as possible" (23, p. 525). In a more remarkable way lie adds: "Thereby has resulted the furnisliing of a fixed basis for a thorough quantitative and qualitative analysis of marine organisms." According to my view such "fixed basis" was obtained long ago, particularly by the widely extended investigations of the Challenger expedition (from January, 1873, to May, 1876), fitted out with all appliances. This embraced a period of forty months, and included " the whole expanse of the ocean." Their experience ought to lay claim to much greater value than that of .the Ifat ion al, whose voyage of three months took in only a part of the Atlantic, and was in addition trammeled by bad weather, accidents to the ship, early loss of the large vertical nets, and other misfortunes in the carrying out of their plans. It is hardly conceivable how an "exact investigator," from so incomplete and fragmentary experience, can derive the "fixed basis" for new and far-reachiug views, which stand in remarkable contradic- tion to all previous experience.

It would here lead too ftir, if, from the numerous old and new narra- tives of voyages, I should collect the observations of seafarers ui)on the remarkable inequality of the sea population, the different fauna and flora of the regions of currents, the alternation of immense swimming swarms of animals and almost uninhabited areas of sea. It is sufficient to ])<)int out the two works in which the most extensive and thovougli knowledge up to this time is collected, the " iTarrative of the Cruise of

H. M. S. Challenger,^'' edited by John Murray (6), and the " Collezioni della E. Corvetta Vetfor PisanP'' (8), published by Chierchia. Since the general chorological and cecological results in these two principal works agree fully with my own views gained from thirty years' experience, I pass immediately to a general exi)osition of these latter, reserving their proof for a later special work.

A. —POLYMIXIC AND MoNOTONIC PLANKTON.

The constitution of the planMon of swimming plants and animals of different classes is exceedingly manifold. In this regard I distinguish first two principal forms, polymixic and monotonic plankton.* The "mixed tow-stuff (J. w/ifr/ei), or the polymijcic planJdon,''^ is com- posed of organisms of different species and classes in such a way that no one form or group of forms comi^oses more than the one-half of the whole volume. The ^'simple tow-stuff", on the other hand, or the monotonic planlton,''^ shows a very homogeneous composition, while a single group of organisms, a single species or a single genus, or even a single family or order, forms very predominantly the chief mass of the cai)ture, at least the greater part of the entire volume of the plankton, often two- thirds or three-iburths of it, sometimes even more. Under this mon- otonic plankton one may again distinguish prevalent planlcton, when the predominant group forms up to three-fourths of the total volume,

* n.o?ivniKToc = mucli mixed, complex; uovurovog = of a single form, simple. PLANKTONIC STUDIES. 609 and uniform planUon when this exceeds three-fourths and forms ahnost the whole mass. In general the mixed plankton is more abundant than the simple, condi- since as. a rule the circumstances of the "strug-o-le for existence" tion and vary in many ways the constitution of the planktonic flora and fauna. Still there are numerous exceptions to this rule, and at many points in the ocean (especially in the zoocurrents) there occurs locally or a development so numerous, and an accumulation of a single form group of forms in such swarms, that these in the haul of the pelagic net form more than one-half the entire volume. This monotonk' planldon appears in very different definite forms; for the difterence of climate, the season, the oceanic currents, the neritic relation, etc., determine significant differences in the quantitative development of the plankton organisms, which simultaneously appear in vast numbers in a definite region. I will next briefly go over the single forms of the monotonic of the l^lankton known to me, passing over, however, the consideration extremely manifold composition of the pohjmixic planlcfon, since I am reserving that as well as a contribution of a number of mixture-tables for a later work. of pelagic 1. Monotonic rrotoplnjtic PlanMon.—Oi the seven groups Protophytcs, at least three, the Diatomic, Miwracytes, and Peridinew, constitute appear in such quantities in the ocean that they alone may the larger part of the collection of the pelagic nets. The most impor- tant and most common is the monotonic diatom-planMon, particularly in brackishand coast waters. Tlie siliceous-shelled unicellular Profophi/fcs which compose this belong, often predominantly or almost entirely, to in tlie a single species or genus, as Syncdrc in the colder, Chwtoceros diatoms, warmer seas. The colossal masses of Arctic and Antarctic which form the "black- water," the feeding-ground of whales, have been mentioned above. In the warmer tropical and subtropical parts of occur. Here the ocean such accumulations of diatoms seldom or never composed of their place is taken by the monotonio murraciite-planUon, immense swarms of nyctipelagic Pyrocystidw. Less frequent is the monotonic pcridinexv-pJanUon. Although these THnofiageJlaia take a plank- very significant part in the composition, especially of the neritic as to form the ton, yet they do not often occur in such quantities greater part of the volume of the capture. pelagic Metaphytes 2. Monotonic Mefaphytic-Planlcton.—Among the which there are only two tbrms, the Oscillatoriw and the Saroassew, pelagic appear so numerously that they form the greater part of the formed of t

3. Monotonic Protozoic-Flanldon.—Among the miicelliilar Protozoa^ three different groups, the Woctilaca, (Mohigerina, and Eadiolaria, ap- pear pehigically in such quantities that they form the greater part of the volume of the plankton. The monotonic noctiluca-planMon is neritic, and is com])Osed almost exclusively of milliards of the common Nocti- luca miliaris. It forms the reddish-yellow covering of slime upon the surface of the coast seas, and in the ocean always points out the litto- ral currents. On the other hand, the widely distributed monotonic ylo- Mgerina-planlton is purely oceanic, the point of origin o^ theglobigcrina ooze of the deep sea. In different regions of the ocean it is composed of different genera of the above-mentioned pelagic thalamophores. Much more manifold is the monotonic radiolaria-planMon, also oceanic. Of these, one can distinguish the three following modifications:*

(1) rolyci/ttnn'a-PlanlctoH, sometimes composed only of Collozoum^ sometimes of Sphwrozoum, sometimes of Collospluvra, most often of a mixture of these three forms ; in the warmer seas, partly pelagic, partly zonary; very abuiulant.

(2) Acantharia-PlanMon, commonly formed of milliards of a single or of a few species of Acanthonietron (iu the colder seas, e. g., on the east and west coast of South America, south of 4:0^ S. lat. ; also north of jSTorway) partly 50^ K. lat. on the coast of Shetland, Faroe-Orkney, and ; autopelagic, partly bathypelagic.

(3) Phwodaria-Planldon, zonary and bathybic, mostly composed of the larger species of Anlosphwridcv and Sagosphwrida', GoeJodendridcv and

CoelograpJiidcr {e. g., Goeloplcgina murndjanum from the Faroe-Orkney

Channel, 4, p. 1757). 4. Monotonic Gnidaria-PlanMon.—In the group of nettle animals there are numerous forms of medusas siphonophores, ami ctenophores, which appear in immense schools. The monotone medusa-planlcton is chiefly neritic, composed of very different local forms on the different coasts. Of the larger Acraspcdota, in the warmer seas Rhizostoma (Pil- emidw, Cranihessidw) particularly occur; iu tlie colder, Seniostoma

{AnreUdcc, Cyanida'), which in schools fill the littoral bays and cur- rents. Of the oceanic Scgphomednscc, Pelagia seems to form similar schools. Among the Graspedota., monotonic medusa-plankton is espe- cially formed of neritic Gordonidiv, Jirargelidcc, and Uucopida', of oceanic u^qnoridce, Liriojridw, and Trachyncmidw. Monotonic siplionopliora- planldon occurs only in the warmer seas, although Dipliyidea are found abundantly in all parts of the ocean. The remarkable blue troops of the pelagic PhysaUdw, Porpididw, and Velellidxv have for a long time

*Radiolariaii-plankton is contained in 13 preparations of the Radiolaria collection, whicli I have collected (1890) and which can he bought through the famulus Franz Pohle at Jena; 8 of these preparations contain polycyttaria-plankton, 2 acantharia- plankton, and 3 plncdodarin-phiuktou. This collection (of 34 microscopical prepa- rations) cnibraces in addition 17 preparations of the radiolarian-ooze of the deep sea, and 1 preparations of dee]> sea horny-sponges, whose pseudo-skeleton is composed of radioiariau slime. (Challenger Report, part Lxxxii.) PLANKTONIC STUDIES. 611 ill the tropical and subtropical seas attracted the attention of seafarers I)y their immense numbers as well as by the irregularity of their sudden appearance and disappearance. Earer is a purely 'physonectic plank- ton chiefly composed of ForsMUa; I have observed such repeatedly at Lanzarote. At that same place also occurred frequently a monotonic cteno2>hora-pl(inkton. These delicate nettle animals also, as is well known, like the Medusre and Siphonophores, appear in such closely packed crowds that there is scarcely room between tliem for other pelagic animals. Not infrequently the great accumulation of a single species of ctenophore imparts to the planktoii a very reuiarkable char- acter, and this is true in all oceans, in the cold as well as in the warm and temperate zones. More often it happens that the monotonic cnid- aria-plankton is composed of several species of Medusw, Siphonophores, and Cfenophores, while other classes of animals take only a very limited share in its constitution. 5. Monotonic Sagittkkv-Phmlion.—Tlie only form of monotonic plank- ton which the branch of Helminilies furnishes is made up by the class of the Cha'tognatha, various species of the genera Sagitta and Spadella. Although purely oceanic according to their mode of life, yet they occur numerously in the neritic tow-stuff {Auftrieh). Sometimes only a single species of these genera, sometimes several species close together, appear in such swarms as to make n[) more tlian half of the entire plankton. These phenomena have been ol)served in tlie colder as well as in the warmer seas. In tlie former tlie plankton is composed of the smaller, in the latter of the larger species. These forms occur also in the deep sea, and indeed the zonary HagHtUhv-planMon is composed of different species from the pelagic,

f). Monotonic Pteropoda-Planldon.— /vstonishing masses of oceanic pte- ropods are very widely distributed in all parts of the ocean, and in part are formed of characteristic genera and species in the different zones. The immense schools of Clio horcfdis and Limacina arctica, which inhabit the northern seas and (as -'whale-food") furnish the chief food supply for many cetaceans, sea-birds, tishes, and cephalopods, have long been known. But no less immense are other swarms of pteropods, composed of different genera and species, which populate the seas of the temi)erate and tropical zones. These have often escaped the notice of seatarers, because most species are nyctipelagic. Of the immense quantities of these floating snails, direct evidence is furnished by theaccunnilated calcareous shells, which in many stretches of ocean (especially in the tropical zone) thickly cover the bottom at depths between 500 and 1,500 fathoms. Often the greater part of this " pteropod-ooze " is formed solely of them (G, pp. 120, 922). At Messina as well as at Lanzarote I found the pteropod-plankton often mixed with considerable numbers of heteropods. Still the latter never form the greater part of the volume. 612 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

7. Monotonic Crustacea -Phmlcton.—As the crustaceans surpass all other classes of the animals of the x)lankton in quantitative develop- ment, so they form monotonic plankton far more often than all other classes. Most commonly this simple crustaeean-phinkton is composed of copep'ods, not infrequently entirely of a single species (6, pp. 758, 843). Next to this I have more frequently found monotonic osiracoda -plank- ton; next schizopoda-planMon. Sometimes also there are in these two orders only numberless individuals of a single species, sometimes of many different species, which compose the monotonic plankton, often almost exclusively, and at other times nuxed with additions of other Crustacea, Sagitta, SaJpa, etc. The other above-mentioned orders of crustaceans, which also- ta-ke a considerable part in the constitution of the plankton, the decapods, amphipods, and phyllopods, I have never found in such quantities that they formed more than half of the mass of tow-stuff. On the contrary, such quantities of crnstace^in-Iarva' of one species (e, g., of Le^jas and other cirripeds) occasionally appear that they predominantly determine the character of theplaiditon. 8. Monotonic Tanicata-Flanldon.—Next to the monotonic forms of plankton, which are comj)Osed of Crustacea and Gnidaria, tliat of the Tunicata m most numerous. Quite preponderant in quanlity are the ThalUliw or iSalpacea' (Salpa and ^SaJpeUa), and among these, especially the smaller species {Salpa dcynocratica-mucronata, S. runcinata-fusi- formis, and related species). I have often taken such monotonic salpa- planLion in the Mediterranean, in the Atlantic and Indian oceans, and have received the same also through Capt. Kabbe from different parts of the Pacific Ocean. Masses of Doliolum and of Copelata {Appendicu- laria, VexiUaria^ etc.) are also commonly mixed witli this in greater or less quantities. Still these planktonic tunicates, on account of their small size, recede before the Salpa'. I know of no instance where they have by themselves formed a monotonic plankton. But this is the case with the nyctipelagic pyrosoma. The (JlialJengcr and tlie Yettor Fisani in the tropics, on dark nights, met with quantities of monotonic pyrosoma-planlcton in the middle of the Atlantic and Pacific. By day not a single one of these "cones of fire" was to be seen, and as soon as the moon arose they went into the depths (8, pp. 32, 34). 9. Monotonic Fish-PlauMon.—If, with Ilensen, we limit tlie term plankton to the halohios floating x>assively in the sea, we can desig- nate as "monotonic fish-plankton" only the schools of very young and small fishes, which often ai)pear abundantly in the currents, occasion- ally so compact that very few other pelagic animals can find room between them. If one wishes to extend the term still farther, and wipe out the sharp distinction between planMon and neMoUj all those sea fishes (oceanic as well as neritic) which appear in schools, and which play so significant an oecological role in tlie cycle of matter in the sea

{e. g., ScopcUda', Clup>eida\ Leptocephalidfe, Scomberoida') will in general belong here (12, p. 51). —

PLANKTONIC STUDIES. 613

B. Temporal Planktoxic Differences.

The first and most remarkable pheiiomenou, known to every seafaring plauktologist, is the varying- constitution of tlie plankton and tlie vari- able mingling of its constituents. The remarkable differences of com- position apply qualitatively and quanUtaUvely to the oceanic as well as to the neriUc plankton. They are just as im])<)rtant in the comparison of different places during the same time as at different times in one and the same ])lace. We can therefore distinguish h)cal anil temporal variations, and will first of all consider the latter. To obtain a complete and more certain survey of the temiDorary vari- ations of plfinktoii comi)ositiou, there would be needed especially an unbroken series of observations, which had been carried on at one and the same place at least for the space of a full year—still better for several successive years—to obtain from the yearly and monthly oscil- lations a general average. Such complete series of ohservations, com- parable to the meteorological (with which they stand in direct causal connection), have not hitherto been made. Tliey belong to the most im- portant tasks ofthe zoological stations now everywhere springing up.* Meanwhile, a general conception of the considerable size of the yearly and monthly oscillations can be obtained from a comparative summary based upon the important series of observations extending over three years, whi(;h Schmidtlein has given u{)on the api)earance of the larger l^elagic animals in the (iulf of Naples, during 1875-77 (19, p. 120). The contributions of Graeffe upon the occurrence and time of appear- ance of marine animals in tlie Gulf of Trieste are also worthy of notice in this connection (20). The considerable temporal variations which underlie the appearance of the i^elagic organisms and which determine such great differences in the plankton composition, relative to quality and quantity, may be divided into four groups: (1) yearly, (2) monthly, (3) weekly, (4) hourly variations. Their causes are manifold, partly meteorological, partly biological. They are comparable to corresiionding temporal oscillations of the terrestrial flora and fauna, on one side depending upon climatic conditions and meteorological processes, and on the other upon the changing mode of life, especially upon the conditions of reproduction and development. As the annual development of most terrestrial plants is connected with definite time conditions, as the period of bud- ding and leaf development, of their blossoming and fructification, has

* My own extensive experience, I am sorry to say, is in this regard very Insufficient, since I have never worked at a zoological station, and since usually I was only so fortunate as to go to the seacoast for a few months (or even only for a few weelis) during the academic vacation. Only once have I had the opportunity to extend my plankton studies at one and the same place to a half year (from October, 1859, to

April, 1860, at Messina, 3, p. v, 166), and three times have I carried them on for three months at the same place—in the summer of 1859 at Naples, in the winter of 1866-67 at Lanzarote, and in the winter of 1881-82 in Ceylon. —

614 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

become adai)te(l to the meteorological coiKlitions, the time of year and otlier conditions of life in tlie " struggle for existence, " so also tlie annual development of most marine aninmls is governed by definite, inherited habits. With them also the intiuence of meteorological vari- ations on the one side, of oscological relations on the other, are of the greatest importance for the periodical appearance. Most organisms aijpear in the plankton only periodically, and only very few can be reckoned as belonging to the " perennial plankton" in Hensen's sense

(9, p. 1). This investigator also attaches great importance to the tem- poral "highly remarkal)le variations'' in the plankton composition (9, pp. 29, 59); he explains it in part by " periods of famine" (p. 53). Yearly oscillations.—The i)lankton literature has hitherto contained only a few reliable statements upon the yearly variations, which underlie the appearance of the pelagic animals and plants. Still there are a few contributions of liigh merit, extending over a series of years, namely those of Schmidtlein irom Naples (19) and of Graeffe from Trieste (20), Even the first glance at the tables, those of the former relating to the ai)pearance of the i^elagic animals in the Gulf of ISrai)les, shows us how remarkably different was the action of the majority of these in several successive years. As there are good and bad wine and fruit years, so there are rich and barren plankton years. But Schmidtlein correctly remarks that extensi\e observations extending through a long series of years are demanded to gain a deeper insight into the meaning of these yearly and monthly variations shown in the tables. The same view is also held by Chun, Avho, in his monograph of the

ctenophores of the Gulf of Naples (p. 236), points out how very differ- ent was the number of these in five successive years. Graeffe, resting on the basis of his observations for many years, says of CotylorMza tuberenlata, that this beautiful acaleph has not for many years been found in the Adriatic, in other years only individually, but not at all rarely (yet always only in the three months of July, August, and September). Just as variable is the occurrence ^^ according to the year''''—of Umhrosa lohafa and other medusa^ Of the six species of ctenophores of the Gulf of Trieste, only one a^ipears every year, the five others only noAv_ and then. Not only do the qnantities of individuals, but also the " time of appearance of pelagic animals change according to the meteorological conditions of tlie time of year" (20, v, p, 361). I myself can fully establish this proposition on the ground of observa- tions which 1 have made in the course of many years of medusa studies. Many of these "capricious beauties" occur in one and the

same place on the Mediterranean coast {e. g., in Portofino, in Viila- franca), numerously in the first year, rarely in the second, and not at all in the third. When, in April, 1873, 1 fished in the Gulf of Smyrna, it was full of swarms of the great i)elagic Chrysaora hyoscella. In April, 1887, when for the second time I sought the same gulf, I could not find a single individual of that beautiful medusa, but instead the PLANKTONIC STUDIES. 615 g-ulf was tilled by crowds of a new, hitherto uudescribed, large medusa, Drymonema eordelia. Thousaiid.s of these Cijaneidw lay cast upon the beach at Cordelio.* MoHthUj oscillations. —The time of year is of Just as great imi^ortauce for the appearance of very many i>elagic animals as for tlie liowering and fruit formation of laud j)lauts. Many of the larger planktonic ani- mals, Medusw, Siphonophores, Gtenophores, Heteropods, Fi/rosoma, etc., appear only in one month or during a few montlis of the year. They form Hensen's "periodic plankton." In the Mediterranean many pelagic animals are numerous in the winter, while in the summer they are entirely wanting'. This "periodical ai)pearance of pelagic animals" has long been known and often mentioned; but not so tl^e important fact that these ethoral periods themselves show considerable variations. For tliis the tables of Schmidtlein (19) and the notes of Graeffe (20) give important points of support. Especially the DisconecUv and other Siphonophores\ behave very irregularly. The cause of the monthly variation lies on the one side in the conditions of reproduction and develoi>ment; on the other in the varying temperatTU-e of the season, as Chun has lately Shown (15, 16). Daily oscillations. —Every naturalist wh.) has observed and fished pelagic aninuils and plants in the sea fov a long time, knows how uidike their appearance is on different days in the same period of the year or in the same mouth, when one may daily hope to find them. As a rule, the weather, and particularly the wind, conditions tlie remarkable

* Driihionema eordeVm, whose milk-white iiml)rella. reache.s halfii meter in diameter, I will describe liereafter. It differs! in the formation of tlie gonads and oval tenta- cles, as in several other points, Irorn the Adriatic species, which I have described as

Drtjmonema victoria {^= (lalmaiinum) (ii, 29).

f Of the Disconectce (Poiyita and VcJella) Chun during a 7 months' residence at tlie Canary Islands (1887-88) conld find not a single specimen. According to him they should appear first in midsummer (July to September). On the other hand I saw at Lanzarote an isolated swarm of these Diseonectw in midwinter, in Feb- ruary, 1867. —

61 G REPORT (5F commissioner OF FISH AND FISHERIES.

Hourly osciUailons.—Manj' pelagic auiuials appear at the surface of tlie sea only at a definite hour of the day, some in the morning, others at noon, still others towards evening. During the remainder of the day uot a single individual of the species is to be found, Agassiz, thirty years ago, brouglit forward noticeable examj^les of this from the class of Medime, and I can from my own experience adduce a number of other examples. But many other pelagic animals also

{e. g., Sq)honophorc.s', Reteropods) come to the surface only for a few hours. We have long known that the swarms of the nyctipelagic Fteropods, Pyrosoma and many Crustacea, come, to the surface only during the night and flee the light of day. Other groups act Just reversely. But the late extensiye observations, especially of Murray (0), Ohierchia (8), and Chun (15) have taught us how great is the (extent and importance of those hourly variaticms. That these are of great influence upon the composition of the plankton, and that this accordingly is very different at different times of day, needs n > repetition. But we must allude once more to liow all these tiimporal oscillations must be taken into consideration, if the equality of planlton distrlhution is to be proved by observation and estimation. In point of fact they all seem to tend to very remarkable Inequality.

C. Climatic Plankton Differences.

The mimerous contributions which earlier and later observers have made upon the appearance of the swarms of the pelagic aniuuils in different regions of the ocean, agree in pointing out the differences among them, corresponding to tlse climatic zones. Thus the Arctic oceans are characterized by masses of monotonic plankton of Diatom, .Beroidw, Gopepod, and Fteropod groups, swarms which are often com- l)osed of milliards of single species. In the oceanic regions of the temperate zone we meet monotonic plankton of the Facoid, Kovtiluca, Medusa, Ctenophore, Salpa, Scliizopod, etc., classes, sometimes com- posed of one, sometimes of several species. In the tropical ocean im- mense banks of monotonic plankton appear, in which the Murracytes, OsciUatoriic, FhysaUa, Fyrosoma, Ostracoda, determine the character of the swimming oceanic population. Although these facts have long been known, up to this time no attempt has been made to arrange them chorologically or to define more closely the characteristic features of the plankton in the climatic zones. Yet I believe, partly ui)on the ground of the ac( ounts referred to above (particularly of the Challenger and of the Vetfor Fisani), imrtly on the ground of my own comparative investigations (of the Challenger as well as of the Rabbe collections), that even now an important proposition can be formulated. The quantity of the planldonis little dependent upon the climatic differ- ences of the zones, the quality very dependent; especially in this tcay, that the number of component species diminishes from the equator towards both poles. This i)ropositiou corresponds, on the whole, with the con- ditions which the climatic differences show in the terrestrial fauna and PLANKTONIC STUDIES. 617

tiora. Here as there the explanation of the facts is above all to be sought in the intluence of the sua, that -'all-powerful creator," which

in the tr()i)ical zone conditions a much more lively interaction of the natural forces than in the pcdar zones. The ''cycle of matter in the sea" {Stoffwechsel cles Meeres) is no less influenced by the perpendicular rays of the sun than is the terrestrial f\iuna and flora; and as in the tropics the quantity and the complexity of the terrestrial organic living forms is by far most highly developed, so is it also the case Avith the marine forms. Hensen places himself in remarkable opposition to this hitherto accepted view when in his account of the results of the Xafional expe- dition he suri)rises us^with the following statement:

Altliongli \Ye have found plankton everywhore, the amount of it under and near the tropics Avas relatively small, namely on an average 8 times less than in the north near the Banks of Newfoundland. Each one of these hauls contained upwai'ds of a hundred different forms; hut the poverty of the (juantity is still a remarkably ajiparent established fact (22, \). 245).

In the notable account which E. du Bois-Reymond (on January 23, 1890) laid before the Berlin Academy \\-pon the results of the National expedition, it was said concerning its scientitic results that a complete account could not be given for three years, but then he added:

Only one chief result may here be assumed beforehand. Contrary to all expecta- tions, established upon a theoretical basis, the quantity of plankton in the tropical Avaters is shown to be surprisingly small (21, p. 87). Since Hensen with this "chief result" of the National expedition stands in strong opposition to the familiar experience of the Challenger, of the Vettoi' Phnnl^ix^d of many other exi^editions, we must first of all again examine the empirical foundations upon w^hich his assertions rest. For these he admits that he regards as such only the results of his ''trial trip^'' through a part of the Atlantic ocean, in which the resi- dence in the tropics embraced scarcely two months. The results which he here draws from his plankton fisheries, which obviously turned out remarkably poorly as a result of accidental conditions, may contradict the results which were set up by the Challenger and the Vettor Fisani during a residence in the tropics of altogether four years, in different parts of three great oceans. It is not indeed saying too much, if we declare this kind of conclusion by Hensen as hasty, and the "exact method" which he wishes to establish by computation as useless. My own comparative study of the rich planktonic collections which Murray and Rabbe have brought in from the different parts of the three great oceans, has convinced me that the tropical ocean is not only qual- itatively much richer (by the variety and number of planktonic spe- cies and genera) than the oceans of the temperate and cold zones, but that it also does not fall behind the latter quantitatively (in the abun- dant distribution and vast accumulations of individuals). To be sure, one ought not to take into consideration merely the surface of the trop- ical ocean (although this also is often extremely densely populated), but 618 REPORT OF COMMISSIONER OF FISH AND FISHERIES. also the deeper zonary regions. For in tlie tropical zone tliere are numerous nyctipelagic organisms, whicli by day sliun the glow of the I)erpendicular rays of the sun and betake themselves into the cooler, more or less deep layers of water; but at night these bathypelagic ani- mals and plants jippear at the surface in such immense crowds tliat they are not surpassed in quantity by the "immeasurable swarms" of pelagic organisms in the temperate and cold zones. During' my trip through the tropical region of the Indian Ocean, as well on the way to Ceylon (from Bombay) as on the return (from Soco- tora), I daily wondered at the great richness of pelagic life on the mir- rored surface. At night the ''Avhole ocean, as far as the eye could see, was a continuous shimmering sea of light" (25, p. 52). The luminous water, which at night we scooped up directly from the surface with buckets, showed a confused mass of nyctipelagic luminous animals {On- tracods, tSaljia, Pyrosoma, Medusw, Fyrocystcc), so closely packed that in a dark night we could plainly read the print in a book by the bright- ness of their pelagic light. The crowded mass of individuals was not less considerable than I have so often found in the Mediterranean in the currents of Messina. What quantities of food the plankton must here furnish to the larger aniuials was shown by the vast schools of great medusre and flying-fish, which for days accompanied our vessel; and this mass covered large areas of the open Indian Ocean, midway between Aden and Ceylon. Just such i>lanktou masses I have received through the kindness of Capt. llabbe from other tropical parts of the Indian Ocean, between Madagascar and the Cocos Islands, and be- tween these and the Sunda Archipelago, I encountered a wonderfully rich and thick planktonic mass in a iielagic current of the southwest monsoon drift, 50 nautical miles south of Dondra Head, the southern point of Ceylon.* I have referred to the richness of this in my " Indian

Journal" (25, p. 275). That the tropical zone of the Atlantic Ocean also possesses a vast wealth of plankton is shown by many older accounts, but especially from the experience of the Challenger. In the middle of the Atlantic, between Cape Verde and Brazil, Murray observed colossal masses of pelagic animals; and if by day they were scarce at the surface, he con- tinually found them below the surface, in depths of 50 to 100 fathoms sur- and more (0, pp. 195, 218, 27G, etc.); at night they ascended to the face and filled the sea far and wide with a brilliant glow (pp. 170, 105, etc.). '' On the ichole cruise along the Guinea and equatorial currents, the pelagic life teas exceedingly rich and varied, in the quantities of individ- uals as well as of vspecies, onueh more than anywhere else in the northern or soutliern part of the Atlantic Ocean. The greatest quantities were seen in the Guinea current during calms, when the sea literally sicarmed

*A part of the new species of pelagic animals wliich I found in this astonishingly rich oceanic current arc described in my ' Keports on the Siphonophora and Kadio- laria of H. M. S. Challenger." PLANKTONIC STUDIES. 619 with life'" (p. 2iS). This astonisliing wealth of i)laukton was observed in the wliole breadth of the Atlantic tropical zone in Angiist and Sep- tember, 1873; bnt it was not less than that passed by the Gltnllenger on her return in March and April, 187G, in the eastern part of the same region, between Tristan d'Aonnha and Cape Yerde. "When the water was calm, an extraordinary siiperabnudance of pelagic life appeared at the snrface. O.^clllatorice covered the sea for miles, and vast quantities of Badiolaria [Gollosoun) filled the nets" (p. 930). With those and other accounts by the Challenger, those of tiie Vettor Flsani quite agree.

" T'nc zone of eiimitorial calms is out ofaUjjrojjorlion rich in organic life. Sometimes the' water seems coagulated, jelly like, even to the touch. It is impossible to describe the quantities of variously colored forms"

(8, p. 31). Chiercliia enthusiastically describes the wonderful spectacle which the luminous ocean furnishes at night—"a sea of light which ex- tends to the whole horizon" (pp. 32, 53, etc.). The iiumerous plankton samples wiiich I myself have investigated from the Atlantic tropical zone show for the most part an extraordinarily rich composition, par- ticularly those between Asceusion and the Ganarj? Islands {Challenger stations 315 to 353), above all the two equatorial stations 317 and 318, which, like the Canary currents, which I studied for three months at Lanzarote, whose fabulous wealth I have already mentioned, also belong to the region of the iroplcal trades-drift. Tiie quantity and wealtli of forms of the plankton in the tropical zone of the Pacific Ocean is not less than in the tropical region of the Atlantic and Indian oceans. In the most diverse parts of this region the Challenger sailed tlirough "thick banks of pelagic animals," Between the iSTew Hebridiis a id ]S"ew Guinea "the surface of the water and its deeper levels swarmed with life. All the common tropical forms were found in great abundance. The list of genera of animals was about the same as in the Atlantic tropical region (i)p.218, 219), but it showed consideraMe diiference in the relative abundance of species''^ (0, p. 521). Among the Philippines the water showed "a quite uncom- mon quantity and variety of oceanic surface animals" (p. CC2). On the voyage from the Admiralty Islands to Japan the oceanic "fauna and flora of the surface was everywliere especially rich and varied. In the neighborhood of the equatorial countercurrents, between the equator and the Carolines, pelagic foraminifera and mollusks were taken iii such quantities in the surface net that they surpassed all earlier observations," etc. (p. 73S). On the voyage through the ce«f>v(i part of the tropical Pacific, from Honolulu to Tahiti, between 20° ]Sr. hit., and 2i)'^ S. lat., "the catch of the tow net was everywhere very rich. The superahundance of organic life in the equatorial current and countercurrent is very noticeable, as well with reference to the number of species as of individuals''' (p. 776), From this wonderfully rich region, which of all parts of the tropical ocean is farthest removed from all continents, came the absolutely richest plankton samples which I have 620 REPORT OF COMMrsSIONER OF FISH AI7D FISHERIES. ever studied, those which the Challenge)- brought from her stations 262-280, My astDiiishiuent was great when I first saw these planktonic masses, in the autumn of 1876; but it grew boundless when a year later I studied iireparatious talcen from them aud found in them hun- dreds of new species of pelagic animals. The wonderfully rich Badiolaria ooze which the ChaUenger brouglit up at the central Pacific stations 263-274 (from depths of 2,000 to 3,000 fathoms) is only the siliceous remains of that planktonic mass, from which all organic constituents have vanished and the calcareous shells for the most part dissolved by the carbonic acid of the deep currents.* The numerous surface preparations which Murray finished npon the spot on this remarkable voyage of planktonic discovery through the central Pacific, and mounted in Canada balsam, are ahsolutely the richest planJc- ton preparations which I have ever studied, especially those of stations 266-274, between 11° N. lat. aud 7° S. lat. The richest of all stations is 271, lying almost under the e(pmtor (0o33'S. lat., 152o 56' W. long.). I have since shown these pre^jarations for microscopical studies to many colleagues aiul friemls, and they have always expressed the liveliest astonishment over the new " wonder- world " concealed in them. They are jokingly called tlie "mira-preparatious" (comp. 4, §§228-235). The wonderful planktoa v/ealth of the tropical Pacific is as well established by the mauifold observations of Chierchia: " The quantity and quality of the organisms tchich inhabit the tropical regions of the sea surpass all conceptions^ (8, p. 75). Inconceivable quantities of pelagic animals of all groups were seen in the middle of the tropical Pacific, between Callao aud Hawaii, between HonoluUi and Hongkong, not only at the surface, but in the most various depths up to 4,000 meters. The quantity of deep-sea siphouopliores was here so enormous that the sounding lead was never drawn up without its being surrounded with torn-off tentacles (p. 85). During the forty days' voyage from Peru to Hawaii the pelagic fishery at tlie surface as well as in tlie depths brought to light *'suc]i a quantity of different organisms that it must seem almost impossible to one who did not follow the work witli his own eyes" (8, p. 88). Similarly, in the Chinese sea and in the Suuda Archi- pelago immense masses of plankton were encountered. It is my intention here to bring together the most general impres- sions of the relative planktonic wealth of the various oceanic regions, which I have gained from a comparative study of many thousand planktonic preparations. The iselagic fauna aud flora of the tropical zone is richer in different forms of life than that of the temperate zone, and this again is richer than that of the cold zone of the ocean. This is true of the oceanic as well as of the neritic plankton. Everywhere the neritic plankton is more varied than the oceanic. The wealth of

*0f this Badiolaria ooze there are 16 saniijles (embracing about 1,000 dilfereut species) coutaiued in the " Radiolariau collection " (1890) above mentioued. The 8 richest of these (Nos. 20-27) belong to the tropical central Pacific (stations 265-274). ;

PLANKTONIC STUDIES. 621 individuals can in none of these regions bo ciiUed absolutely greater than in the others, since the quantitative development is very depen- dent upon local and temporal conditions and, according to time and place, is on the whole extremely irregular. Estimation of individuals can in this relation prove nothing.

U. —CrUHEXTIC PlANKTONIC DiKl r>KKNCES.

By far the most important of all the causes which determine thfe changing- and irregular distribution of the plankton in the sea are the marine currents. The fundamental imi)ortance of these currents for all planktonic wStudies is generally recognized and has lately been men- tioned many times and explained by Murray (0) and Chierchia (8). Even the zo()logists of the plankton expedition of Kiel have not been able to close themselves to this intelligence. Brandt calls special attention to "the importance of the marine currents as a means of, and limit to, the distribution of the planktonic organisms," so that in the various Atlantic currents numerous forms continually appear which were want- ing in the regions previously traveled" (23, p. 518). Thus, Heuseu mentions the "extraordinarily large i)lankton catches, which were transported by various currents." I learned thirty years ago to recognize the great importance of the marine currents and their direct influence upon the composition of the plankton, when at Messina I went out almost daily in the boat for six months to secure the rich i^elagic treasures of the strait (3, p. 172). The i)eriodical strong marine current, which there is known to the Messinese under the name of the current or the Eema, enters the harbor twice daily and brings to it inexhaustible treasures of pelagic animals which since the time of Johannes Miiller have aroused the wonder and desire for investigation of all naturalists tarrying there. Not less important did I find later the planktonic importance of the local marine currents (at Lanzarote), when the "Zain" current of the Canary Sea in like manner brought with it an extraordinary wealth of pelagic animals. My companion on the trip, Richard Greefr', has very vividly described these marine currents as "animal roads" (IS, p. 307). Dur- ing my numerous pelagic journeys on the Mediterranean it was always my first care to investigate the conditions of the currents, and on the most different parts of its coast (from Gibraltar to the Bosporus, from Corfu to Rhodos, from Nizza to Tunis, I have always been convinced of the determining influence which they exerted upon the composition and distribution of the plankton. Although the fundamental importance of the marine currents for the diverse questions of oceanography are now generally recognized, still very little has been done to follow out in detail their significance for planktology. It seems to me, we must here, with reference to our theme, particularly distinguish {1) Judicurrcnts (the great oceanic currents)

(2) the hathycurrents (the manifold deep cuiTents or undercurrents); 622 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

(3) the veroGHrrents (the littoral ciirreiits or local coast currents); aud

(4) the zoocurrents (the local phmktoiiic streams or very crowded animal roads). Ralicurrents or ocean streams.—The unequal distribution of plank-. ton in tiio ocean is in great part the direct result of the oceanic currents. In general the proposition is recognized as true that tlie great ocean streams, which we briefly designate as halicurrents, effect a greater accunuilation of swimming organisms and thereby are richer in i:)lankton than the /m^/.stesa or "still streams,'' the extensive regions which are inclosed by them and relatively free from currents. For a long time (lie richness in i)lankton which characterizes the Giilf Stream on the east coast of Xorth America, the Falkland Stream on the east coast of South America, and the Guinea Stream on the west coast of Central Africa, has been known. Less understood and investi- gated thaji these Atlantic streams, but also very rich in varied plankton, are the great streams of the Indian and Pacific oceans, the Monsoon Stream on the south coast of Asia, the Moziunbique Stream on the east coast of South Africa, the Black Stream of Japan, the Peru Stream on the west coast of South America, etc. It is very difficult, from the numerous scattered accounts of the pelagic fauna and flora of these great ocean currents, to form a general picture of them, but it is now possible to draw Irom them the conclu- sion that generally the i)lanktou of the halicurrents, qualitatively as well as quantitatively, is richer than the plankton of the haUstasa, or the great oceanic sea basins around which flow the great streams and counter streams, and which meet the first glance on every recent map of the marine currents.* In defending this proposition I rely especially upon the rich experi- ence of the two most iraportaut plankton expeditions, of the (JhaUcnfjer

(6) and of the Vettor Pisani (8), and also upon my own comparative study of several hundred plankton samples, which were collected in part by Murray, iu part by Capt. Rabbe, in the most diverse parts of three great oceans. The planktonic wealth of the great halicurrents is most remarkable at the place where they are narrowest, when the masses of swimming animals and plants are most closely pressed together. Highly remarkable here is the opposition which the rich pelagic fauna and flora of the stream forms iu qualitative and quanti- tative relation to the sparse population of the immediately adjacent halistase. As the temperature and often even the color of the sea

* The systeni.itic biologioal investigation of the hnJisinsa seems to uie to form one of the nearest and most pressing problems of planlitology, and also of oceanography. Apart from the smaller and little investigated Arctic and Antarctic regions, iu all five great areas of quiet water ought to ho distinguished, namely: (1) the North licdisiasc Atlantic (with the Sargasso Soa) ; (2) the South Atlantic (between Benguela and Brazil streams); (3) the Indian (between Madagascar and Australia); (4) the North Pacific (between California and China), and (5) the South Pacific halistasq (between Chili and Tahiti). :

PLANKTONIC STUDIES. 623

water in two adjacent regions is remarkably different and often sliarj)ly contrasted, so also is tlie constitution of th\^ir animal and vegetable world. Thus Murray observed a strong contrast between the cool green coast streams and the warmer deep-blue ocean water when the Challen- ger neared the coast of Chili, between Juan Fernandez and Valparaiso, and correspondingly there occurred a sudden change of pelagic fauna, for the oceanic globigerina disappeared and the neritic diatoms, infu-

soria, and liydromedusa^. appeared in greater abundance (0, i^. 833). This change was very remarkable when the Chcdlenger (at station 240, June 21, 1875) h'ft the warm 'Hjlack stream" of Japan and entered

the cold area of quiet water adjacent on the soutli (about 35° IST. hit., 153° E. long".). Great i)olymixic masses of plankton, dwellers in the tirst area, were here killed by the sudden change of temperature and

rei)laced by the monotonic copepodan fauna of the cold halistase (10, p. 758). Also, later, on the voyage through the Japan stream, the plank- tonic contents of the tow net plainly showed the proximity of two dif^ ferent currents. ''In the cold streams there appeared a greater mass of small diatoms, noctiluca, and hydromednsa:' than in the warmer streams where the richer pelagic animal world {Bafliolaria, Olobif/erina) remained the same which the Challenger observed from the Admiralty Islands to Japan." Many similar cases occurred during the voyage, when proximity to the coast or the presence of coast currents was indi- cated by the contents of the tow net (0, p. 750). Observations upon the plankton richness of the oceanic currents, similar to those of Wyville Thompson and Murray on the Challenger

(6) were made by Palumbo and Chierchia on the Vettor Pisani. The latter calls attenti

It is a fact, that f^onorally ou a voyage tlircngli the ocean great quantifies of indi-

vidiiah of one sjiccies are found pressed fof/ethcr in relative! ij small sjiaees, r.ucl this is true of orgnuisms Avhich, on account of their small size, are not capable of extensive movements. In addition, it is also a fact that Avhen the ship is in the midst of the great oceanic currents, the pelagic fishery gives the nio^.t brilliant results (8, p. 109). It is quite certain that the investigation of the distribution of the pelagic organisms can not progress unless aeeompanied hy aj)arallel study of the currents, the temperature, and the density of the tvater (8, pp. 109, 110). Even the participators in the Xational expedition of Kiel could not avoid noticing the great irregularity of planktonic distribution in the ocean and the importance of the oceanic currents in this respect. During the voyage it was noticed that in different Atlantic currents numerous forms appeared continually which were absent in the regions previously traversed

The conditions are much more complicated ( !) than we had hitherto supposed (23, p. .518).

But it is worthy of notice how Hensen, the leader of this plankton expedition, has noticed this abundant accumulation of pelagic organ- 624 REPOKT OF COMMISSIONER OF FISH AND FISHERIES. isms iu single regions of currents, and lias twisted it in favor of bis theory of the regular distribution of the ])lanMon: The tests of the volume of the plankton show that, five times in the north, once north of Ascensiou, extraordinarily laryv catches ( !) were made. These must have been caused by various currents in this regiou, and can therefore be left out of consider- ation (9, p. 249). It seems to me that Hensen would have done better to take into consideration these Jind other facts observed by him relative to the unequal plankton distribution before he built up his fundamental, certainly adequate, theory of the equality of the same. This was to be expected, since he himself in his first oceanic plankton studies (1S87) observed mauy 'h'emarliahle inequalities,'^ mid his own tables furnish l)roof of this. While he many times mentions the immense swarms of Medusw and declares this " quite superabundant accumulation to be mysterious," he adds: "such j)lacesmust be avoided in this fishery" (9, pp. 27, 65). When Hensen later, in comparing the different catches of copepods (one of the most important planktoiiic constituents), finds that the distribution of the plankton' in tlic ocean is very irregular and that the constitution of this seems to very strongly contradict his general conceptions of natural life (9, p. 52), he holds it to be best that these catches, which are of "such a different kind, should be excluded from consideration" (pp. 51, 53). Also, in the case of Sagitta, which Hensen reckons with the copepods as belonging to the uniform perennial plankton, he finds "throughout not the equality which one

might exx^ect, but much more remarkable variations" {]}. 59). These "surprising inequalities," "variations even to tenfold," he finds iu case of the Dax)hnid(v (pp. 54, 56) and Hyi^eridw (p. 57), the pelugic larvpe of snails and mussels (pp. 57, 58), Appendicularia and Salpa

(pj). 63, 64), the Medusm and Ctenophores (64, 65), the Tintimioids (p.

68), the Peridinia^ (!>. 71), and even in the Diatoms (p. 82)—in brief, in all groups of pelagic organisms which by the numerous production of individuals are of importance for the plankton and upon which Hensen employs his painstaking method of calculation by quantitative planktonic analysis. If one freely "sets apart from consideration" all these cases of remarkable inequality (because they do not fall in with the theoretically X)i"econceived ideas of the equality of planktonic composition), then finally the latter must be proved by counting. Bathycurrents or deep streams.—Through recent investigations, par- ticularly of Englishmen (Carpenter, Wyville Thompson, John Murray, et al.), we have become acquainted with the great importance of the submarine currents or deep streams. It has been demonstrated that the epicurrents, or the surface streams, furnish us no evidence rela- tive to the understreams to be found below them, which we name bathy- currents. These undercurrents may in different depths of the ocean have a quite different constitution, direction, and force from the over- currents. This is as true of the great oceanic as of the local coast cur- rents. If the more accurate study of marine currents is a very difficult PLANKTONIC STUDIES. 625

subject and great liiudraiices lie, as they do, in the way of exact deter- minations, the same applies especially to the deep currents. New ways and means must first be found for pressing into the dark labyrinth of very complicated physical transactions. Kow we can only say that the bathycurreuts are of great importance for the irregular constitution (lud distribution of the planliton. Since the time when, through the discoveries of Murray (1375), Chierchia (1885), and Chun (1887), we learned to recognize tlie existence and importance of the zonary and bathybic fiiuna, aiul particularly, through Chun, the vertical migration of the batliypelagic animals, tlie complicated conditions of the sub- marine currents must evidently have exerted an extraordinary signifi- cance for planktology. Although we have liitlierto known so little about this subject, yet two points stand out clearly: First, that these are of great influence up(Ui tlie local and temporal oscillations of plank-

tonic composition ; second, that it is an untenable illusion if Hensen and Brandt believe that, by means of tlieir perfect-working vertical plankton net, " a column of water whose height and base area can be accurately determined h;is been completely filtered" (23, p. 515); for one can never certainly know what considerable changes in tlie plank- ton of this colunm of water one or more undercurrents have caused during the drawing up of the vertical net. Nerocurrents or coast streams.—.While the halicurrents or the great ocean streams are influenced in the first place by the Avinds and stand in immediate connection witli the air currents of our atmosi)here, it is only partly the case with the local coast currents, for here a number of local causes, which are to be sought in the climatic and geographical condition of the neighboring coast, work together. In the case of coasts which are much indented, in archiijelagos with numerous islands, etc., the study of the littoral currents ])ecomes a very complicated problem. The physical and geological natural condition of the coast mountains and of the beach, the number and force of the incoming rivers, the quality and quantity of the coast flora, etc., are here important factors. The fishermen, pilots, etc., are very well acquainted with these local coast currents,, which we will briefly call nerocurrents^ and are usually to be trusted in the details. Scientifically these currents sliould be studied more closely in smaller part and less quantity. For planktology they are of very high interest and not less important than the oceanic currents. Next, the above-intimated reciprocal relations of the ncritic and oceanic planlcton are to be taken into consideration. He who for a long time has carried on the pelagic fishery at a definite point on the coast knows how very much the result of this is influenced by the natural condition of the coast, by the course and the extent of the coast cur- rents. Straits like those of Messina and Gibraltar, harbors like those of Villafranca and Portofino, furnish uncommonly rich plankton results, because in consequence of the littoral currents a mass of swimming animals and plants are collected together in a limited space. The vol- H. Mis. 113 10 626 REPORT OF COMMISSIONER OF FISH AND FISHERIES. uine of this planktouic mass thus lieapcd up is often ten or many times greater than that in the immediately adjacent parts of the sea. On the contrary, the i)hiiiktoni(; mass is extraoidinaiily poor in pelagic ani- mals and plants, where by the emptying of great floods a rpiautity of fresh water is brought into the sea and its saltness diminished. Johan- nes Miiller pointed out how very much the result of pelagic fishery was influenced therei)y. Again, on the other hand, the rivers day by day bring into the sea a quantity of organic substances which serve as food for the benthonic organisms, and since the benthos again stands in manifold reciprocal relation to tlie plankton, since the meroplanktonic animals (like the medusre, the pelagic larva) of worms," echinoderras, etc.) are the means of a considerable interchiiiige between the two, so is it easily understood how the distribution of the holoplanktonic ani- mals is also influenced thereby and how irregular becomes the com- position of the plankton. Zoocurrents, or planMonie streams.—Among the most noteworthy and important phenomena of marine biology is the great accumulation of swimming bodies which form long and narrow bands of thickened plankton. All naturalists who have Avorked at the seashore for a long period and have followed the irregular appearance of the pelagic organ- isms know these j)eculiar streams, which the Italian fishermen call by the name " correnti." Carl Vogt, in 184S, pointed out their great impor- tance for pelagic fishery (17, p. 303). For their scientific designation and their distinction from the other marine currents I propose the term Zoocurrents or Zoorema* The pelagic animals and plants are so luimerous and so closely packed in these zoiicurreuts as to resemble somewhat the human popuhition in the busieststreet of a great commercial city. But millions and millions of small creatures from all the above-mentioned groups of planktonic organisms are crowded confusedly together, and furnish a spectacle of whose charm a conception can be formed only by seeing it. If one directly scoops up a portion of this motley crowd with a tumbler, not infrequently "the greater part of the contents of the glass (an actual living animal broth) is composed of the volume of animals, the smaller of the volume of water" (3, p. 171). From a distance these "crowded sea-animal streets'' are usually discernible from the smoothness which the surface of the sea presents, while close beside it the surface is more or less rippled. Often one can follow such an " oil-like animal stream," which usually has a breadth of 5 to 10 meters, for more than a kilometer without finding any diminution of the thick crowd of animals in it, while on both sides of it, right and left, the sea is almost vacant, or shows only a few scattered stragglers. At Messina, as at Lanzarote, the phe- nomena of the zoocurrents were especially x)ronounced. My companion

*Rema (used hi Messiua) is from the Greek pn'ua = current; comp. 3, n. 172 note. :

PLANKTONIC STUDIES. 627 on the trip, Eicliard Greeff, has described the Canary animal streams so vividly that I will here give his description verbatim

Our gaze was directed to the highly peculiar long and narrovs' currents, which are of very especial importance for pelagic fishery with fine nets. If one looks at the calm sea, especially from an elevation over a wide exjjanse of water, here and there are seen strongly marked shining streaks, which intersect the surface as long narrow bands. Their course and place of appearance seem to be continually chang- ing and irregular. Sometimes they are numerous, sometimes only few or entirely absent; to-day they appear here, to-morrow there; some have one direction, others the opposite or crossing the first. Occasionally they run along close to one another and unite in a single stream. If one approaches this streak it becomes evident that here in fact a current prevails different from the movements of the surrounding water, and that thereby is brought about the smooth band-like api^earauce. They give the impression of streams cutting through the rest of the ocean, with their own channel and banks, which, notwithstanding the great variations in the time and place of their appearance, yet 'during their existence, which is often brief, show a certain independence. If one conies upon such streams, which are not too far distant from the coast, he sees that all the smaller, lighter objects which formerly scattered over the surface, floated about or cast upon the shore, were drawn into it. Pieces of wood and cork, straw, alga', and tangle tornloose from the bottom, all in motley procession are carried along in this current. But in addition (and this is for us the most important phenomenon) all the animals belonging in the region of these currents arc drawn in and fill it, often in such great quantities that one is tempted to believe it is not merely the mechanical influence of the narrow stream which has brought about such an accumulation of animals, but that the latter voluntarily seek out these smooth, quiet streams, perhaps in (Connection with certain vital -expressions. A trip ujion such a pelagic animal road furnishes a fund of very interesting observations. We can lean over the edge of the boat and review the countless brightly colored sea- dwellers, sometimes passing by singly, so that we can iusjiect them in their unique peculiarities, sometimes in such thickly massed hordes that they seem to form an unbroken layer of animals for a few feet below the surface. Yet these animal roads, where one meets them in the sea, will always form the most certain and richest mine for the so-called pelagic fauna, although naturally, from their changeableness and their dependence upon a calm sea, they can never be definitely counted upon. Likewise, the origin of these noticeable streams and their significance in the natural history of the sea is still almost completely dark, in spite of the fact that they can be observed in almost all seas and under favorable circumstances daily,- and also are known to the fishermen of Arrecife under the name Za'ni (18, p. 307). Although the zoocurrents seem to occur in the most diverse parts of the ocean, and have often aroused the astonishment of observers, yet a recent investigation of them is wanting. What I know al)out them from my own exi)erience and from the contributions of others is essentially the following: The zoocurrents occur in the open ocean as well as in the coast regions, particularly in the region of those nerocurrents which run in straits between islands or along indented coasts. They are dependent upon the weatlier, especially the wind, and appear as a rule only dur- ing calms. Although in the case of the neritic zoiJcurrents the local course is more or less constant, still it is subject to daily (or even hourly) variations. Their breadth is usually between 5 and 10 meters, but sometimes 20 to 30 meters or more; their length is sometimes only a G28 REPORT OF COMMISSIONER OF FISH AND FISHERIES. few hundred meters, and at others several kilometers. Oceanic animal streams reach much greater extension. Their constitution is some- times polymixic, sometimes monotouic, often changing from day to day. Highly remarkable is the sharp boundary of the smooth, thickly populated animal roads, especially if the less inhabited and plankton- poor wateron both sides is rippled by the wind. What combination ;0f causes produces this vast accumulation is still quite unknown; (certainly wind and weather play a role in it; often, also, the ebb and flow of the tide and other local conditions of the regions, especially local currents. As whirlwinds on laud drive together the scattered masses of dust and smaller objects and raise a column of dust upwards, so may the submarine whirlwind press closely together the l)athy[)clagic l^lanktonic masses and carry them upward to the surface. But xirob- ably, also, in the same connection, complicated

VI.—METHODS OF PLANKTOLOGY.

The new aspects and methods which three years ago were introduced by Prof. Heusen into planktology, and of which I have already spoken, have for their main jiurpose the qHantitative anah/sis of the planlion,

i. e., the most exact determination possible of the quantity of organic substance which the swimming organisms of the sea produce. To solve this subject and come nearer to the question connected with it of the '^ cycle of inatter in the sea," Hensen devised a new mathe- matical method which aims chiefly at the counting of the individuals of animals and plants which populate the ocean. This uew method we can briefly term the ocean'i e j)(>pnlat ion statistics of Hensen. The high value which this indefatigable physiologist attributes to his new arith- metical method is shown by the special mention which he makes of it in his first contribution (9, pp. 2-33), from the wonderful i)atience with which he counted for months the single Biatoms, Fcridinea', Infusoria, Crustacea, and other pelagic individuals in a single haul of the Miiller net, and from the long tables of numbers, the numerical j)rotocols, and records of captures which he has appended to his first plankton volume which appeared in 1887. Any ordinary pelagic haul with the Miiller net or tow net brings up thousands of living beings from the sea; under most favoral)le circum- stances hundreds of thousands and millions of individuals.* How much labor and time was involved in the counting of these organisms (for the greater part microscopic) is shown from the fact that "even the count- ing of one Baltic Sea catch, which is pretty uniform in its composi- tion, required eight full days, reckoning eight working hours to the

*In a small catch, which filtered scarcely 2 cubic meters of Baltic Sea water, were found 5,700,000 organisms, including 5.000,000 mici-oscopic peridiuete, 630,000 diatoms, 80,000 copepods and 70,000 other animals (23, p. 516). PLANKTONIC STUDIES. 629

daj'" (23, p. 516). Meoinvliile Brandt, explaininfi' tlie ''highly original procedure" of Hensen (''turning attention to attacking a problem, the solution of which no one had ever thought of"), remarks, with refer- ence to the foregoing quantitative analysis of the Atlantic i)laidcton expedition of the Xational (1889), ''that the very much more manifold ocean catches will consume presumably twice as much time, and since on the plankton voyage at least 120 such catches were made, then the working out of these (quite apart from the preliminary preparations) will fully occupy an investigator for 120 x 14: days, or about 6 years" (23, p. sio).* Opinions respecting the significance and the value of the oceanic po]»ulation statistics of Hensen are very different. E. du Bois-Key- mond, in his paper before the Berlin Academy (21, p, 83), t attributes to it extraordinary importance, "wherefore the uncommon sacrifice made for it was justified." According to his opinion, the plankton expedition of the Kational, arranged for this purpose, within its defi- nite limits, from the novelty and beauty of its well-described task, assumes a unique i)la(;e, and the Humboldt fund ought to be proud at having been among the first to contribute to its execution" (21, p. 87). On the ground of this honorable recognition, as well as of the great hopes which the naturalist of Kiel himself based upon the results of the National expedition, numerous notices have appeared in German newspapers, disseminating the view that an entirely new field of scientific investigation had been thereby actually' entered upon, and that a further extension of it was of great importance. I am sorry to say that I can not agi'ce with tin's very favorable conception,

DISTEIBI TION OF THE PLANKTON.

The foundation upon which the entire planktonic conception and computation of Hensen rests is the view "that in the ocean the plank- ton must be regularly distributed; that from a few catches very safe estimates can be made upon the condition of Very great areas of the sea" (22, p. 243). As Hensen himself says, he started with this ''purely theoretical view,"^ and he believes that a completely successful result is to be had, because these theoretical premises have been more fully

^According to this; the unfortunate plankton counter would in these 120 catches have to count for over 17,000 hours. How such an arithmetical Danaida? work can he carried through without ruin of mind and body I can not conceive. tin the introduction to this noteworthy paper Du Bois-Reymond says that since 1882 Hensen ''had been mindful that, especially on the surface of the sea, there was found a more unequally numerous population of uunutest liviug forms than had previously been supposed" (21, p. 83). This remark needs correction, because many times in the celebrated log l)ook of the Naiiondl plankton expedition this has been overlooked, and therefore it lias wroiiyly been inferred that Hensen eight years ago was the first to discover the existence and ahunduuee of the pelagic fauna and flora. In fact, for forty-five years they have been the object of wonder and study for numerous naturalists. 630 REPORT OF COMMISSIONER OF FisH AND FISHERIES.

established than could have been hoped. 1 have already shown that this fundamental premise is entirely wrong. The mass of i}lanldon in the ocean is not perennial and constant, hut of highly variable and oscil- lating size. The biological coniiiositiou is very diverse, dependent ui)on temporal variations—year, season, weather, time of day, upon climatic conditions and especially upon the complicated currentic conditions of the streams of the sea, of the oceanic and littoral currents, the deep currents, and the local zoocurrents. A comprehensive and fail- estimation of all these O'cological condi- tions must a priori lead to the couvictiou that the distribution of the 2)lanMon in the ocean must be extremely irregular, and Ave find this "purely theoretical view comi)letely established" a posteriori by the comparative consideration and comparison of all the earlier above- mentioned observations. These can not lie regardetl as refuted by the

opposing view of Henseii; for the empirical basis of the latter is, in regard to its time and place, much too scanty and incomplete. One might perhaps object that the technical methods of plankton capture which Hensen employed gave more complete results than the methods hitherto used; but this is not the case. The recent descrip-

tion v> hich Hensen gives of his technical methods for obtaining plankton

(or pelagic fishery) is very praiseworthy (0, pp. 3 to 14). The construc- tion of the net (material, structure of the net, size of filtration), the management of the catch and of the craft, are there carefully described. The advance of the new technique there realized may indeed serve to carry on the pelagic fishery or plankton ca])ture more productively and more completely than was possible with the previous simpler technical apparatus of planktology; but 1 can not find that one of the projiosed improvements of this pelagic technique shows a great advance in prin- ciple and is at all comjiaiable to the great advance which Palumbo and Chierchia made in 1884 by the invention of the closible net. Besides, I can not understand how the new "plankton net" constructed by Hensen could give more accurate results than the simple "Miiller net" hitherto employed, and the "tow net" used by the Challenger. Such a vertical net Mill always bring up only a part of the plankton contained in the volume of water going through it, and by no means, as Hensen and Brandt believe, is a column of water whose height and base area can be measured with sufficient accuracy perfectly filtered. In this supposition the incalculable disturbances by conditions of cur- rents, especially of concealed deep streams, are left out of account, as already mentioned. Besides, Chierchia has lately shown how unreliable and little productive is the fishery with the vertical net on account of the considerable horizontal swimming movements of the pelagic animals

(8, J). 79). At any rate, the improvements Hensen has introduced into the technical methods of plankton capture are not so important that the remarkable difference between his and the earlier results can thereby be explained. PLANKTONIC STUDIES. 631

OCEANIC POPT'LATION—STATISTICS.

Statistics ia general is kuowti to be a very danoeroiis science, be- canse it is commonly employed to lind from a number of incomplete observations the approximate average of a great many. Since the results are given in numbers, they arouse the deceptive api^earauee of mathematical accuracy. This is especially true of the comi^licated biological and sociological conditions, whose total x)henonu!non is con- ditioned by the cooperation of numerous different factors, and is, therefore, very variable according to time and phice. Such a highly complicated condition, as 1 believe I have shown, is the composition of the plankton. If, as Hensen actually wishes, this were to be sufiliciently analyzed by countiug the individuals, and oceanic population statistics were thereby to be made, then this would only be possible by the forma- tion of numerous statistical tables, which should give results in figures of the plankton fishery quantitatively in at least a hundred different parts of the ocean, and in each of these at least during ten different periods of the year. A single "reconnoiteriug voyage" on the ocean, a single "trial trip," limited in time and place, like the three-months Atlantic voyage of the National expedition, can furnish only a single contribution to this subject. But it can in no way, as Brandt thinks, offer " firm foun- dations" for the solution of this and that "thorough analysis" (23, p. 525). If, also, after six years the 120 catches should actually be counted through (after a labor of more than 17,000 hours), if by statistical arrangement of this numerical protocol, by rational reckoning of their results, a serviceable conce|)tion of the quantity of individuals of the oceanic region investigated should be obtained, then at best this one computation would give us an approximate coiiception of the conditions of population of a very small part of the ocean ; but from it by no means can we, as the investigator of Kiel wishes, arrive at conclusions bear- ing upon the whole ocean; for that purpose hundreds of similar com- putations must be made, including the most diverse regions and based ui)on continuous series of observations during whole years. The zoolog- ical stations would be the best observatories to carry out complete series of observations of this character, not such trial trips as the three-months voyage of the National. *

* In my opinion tlie results of the National expedition of Kiel would bave been quite difterent if it had been carried out in the three months from January to March, inster.d of from July to October. On the whole, the volume of jjlanlvtouic catch, at least in the North Atlantic Ocean, would have more than doubled; in some places it would have been increased many fold. Its constitution would have been entirely different. If the expedition had l)y accident fallen in with a zoocurrent, and its voyage had continued in it for a few miles, the contents of the nets would have certainly been a hundredfold, possibly a thousandffdd, greater. 632 REPORT OF COMMISSIONER OF FI8H AND FISHERIES.

COUNTING OF INDIVIDUALS.

Since the new method of oceanic population statistics introduced by Heusen seeks its peculiar basis in the counting of the Individuals which compose the plankton, and since it finds in this '' counting the only basis upon which a judgment can rest" (9, p. 26), then we must examine more critically this cardinal point of his method, upon which he lays the greatest stress. The counting of the single organic indi- viduals, which compose the mass of the i^lankton, is in itself, quite apart from its eventual value, an extremely difficult and doubtful task. Hen- sen himself has not concealed a part of this great difficulty, and attempts to partly allay the doubts which arise against his whole method.* But in fact these are much greater and more dangerous than he is inclined to admit. WHAT IS AN ORGANIC INDIVIDUAL?

This simple question, as is known, is extremely difficult to answer. If one does not accept all the grades of physiological and morpho- logical individuality, which I have distinguished in the third book of my " GenereJIe Morphologic, "' 1800, there are at least three distinct chief grades to be kept apart: (1) The cell (or jilastid); (2) the person (or bud); (3) the cormus (or colony). t Only among the Protista {Pro- tophi/ta and Protozoa) is the actual individual represented by a single cell; on the other hand, among the Histouti {Mrtaphyta and 3Ietazoa), by

* The fourth part of the "Methodik" in the plankton volnme of Hensen, which treats of "the work on land," (a) Determination of the volnme, (&) the conntin<^

(9, pp. 15-30), is especially worthy of reading, not only hecanse it gives the deeiiest insight into the error ofliis method, but also into his very peculiar conception of a general biological problem. tThe swimming animals and plants whicli com]>os(^ the plankton should in this respect be arranged under the following heads: (r/) Protojihi/ia—among the Vhro- viacecB, Calcocyletv, Mnrracyiew, XaniheUexv, TJiciiiocltw, and Peridiueo', all single cells are to be counted; among the diatoms partly the latter, partly the cenobia or cell aggregates, (b) MeUtpln/ia—among the /frt?os^)/(fl')Y( are to be coTiuted the spherical

Thalli; among the OsciUalorHV the single, thread-like ThaUi ; among tbe Sarr/assa the cormus as well as its buds; but the cells which constitute each thallus and bud are also peculiar, (c) Protozoa —the TnfuHorta {NoeiUuca and Tintinua) as well as the rhizopods {Thalamoplwra and Padiolarta), are all to be counted as unicellular individuals, but among the Pohjcuttaria:, besides the C'ocnohia (colonies of Collozoidw, Sphairozoidiv, and (ollosphwridw). (d) CoeJentcrata—among the Medusa', and Cteno- phorcs, as also among the i>elagic Antkozoa and Tiirhellaria the single persons are to be counted ; among the Sipho^iojihores these as well as the single colonies ; for each person (or each medusom) of a cormus is here equivalent to a medusa, (e) Tunlcata—among the CopeJala, Doliohon, and the generations of solitary tSalpas, the single persons are to be counted; on the other hand, among the Pijrosoma and the Salpa chains, the single cormi as well as the persons which compose them, (/-/i) In all the remaining groups of planktonic animals, in the case of sagitta, mollusks, echiuoderm larv;e, articulates, and iishes, not merely the persons are to be counted, but also the cells which make up eai<-h of these metazoa. —

PLANKTONIC STUDIES. 633

tlio higher unit of the person or of the colony, which is composed of many cells. If we actually wish to cany out exactly the method, held by Henseu as indispensable, of counting the individuals, and wish to obtain useful results for his statistical work, then nothing remains ex- cept a counting of all single cells which live in the sea. For only the single cells, as the '' organic elementary individual," can form the natural arithmetical unit of such statistical calculations and the com- putations based thereon. If Henseu in his long " numerical protocols and comparisons of captures" (9, pp. xi-xxxiii) places close to one another as counted individuals—as coordinated categories—the uni- cellular radiolaria, the cormi of siphonophores and tunicates, the per- sons of medusae, ctenophores, echiuoderms, and Crustacea, the eggs and persons of fishes, then he places together vastly incommensurable bulks of quite different individual value. These can only be compar- able for his purpose if all single cells are counted. But since each fish and each whale in the ocean daily destroj^s milliards of these planktonic organisms, so, in order to gain an ''exact" insight into the "cycle of matter in the sea," the cell milliards which compose the bodies of these gigantic animals must be counted and placed in the reckoning.

ECONOMIC YIELD OF THE OCEAN.

Hansen holds the quantitative determinations of the plankton not only as of the highest importance in theoretical interest to science, but also in practical interest to national economy. He thinks " that we Avill be able to invent correct modes of action in the interest of the fisheries,* only if we are in position to/orm a judgment upon the iiro- ductive possibilities of the sea" (9, p. 2). Accordingly he regards it as the most pressing problem to determine the economic yield of the o(teaii in the same way as the farmer determines the useful yield of his fields and meadows, tlie yearly production of grass and grain. By the counting of the i)lanktonic individuals which Henseu has carried on for a long time for a small part of the Baltic Sea, he thinks he has become convinced that the "entire production of the Baltic in organic sub- stance is only a little inferior to the yield of grass upon an equally large area of meadow land." The farmer determines the yield of his meadows, garden, and field by quantity and Aveight, not by counting the individuals. If instead of this he wished to introduce Hensen's new exact method of deter-

* How the practical interests of the fisheries can be advanced hy quantitative plankton analysis I am not able to understand. The most important modes of action which we can employ for the increase of the lish production of the ocean artificial propagation, increase and xirotection of the fry, increase of their food supply, destruction of the predaceous fishes, etc. —are entirely independent of the numerical tables which Hensen's enumeration of individuals gives. That the number of swimming fish eggs furnishes no safe conclusion upon the nuiaber of mature fish has been pointed out above. ;

634 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

« miuatiou, lie must count all the potatoes, kernels of grain, graiDes, clierries, etc., and not only that, Le must also count the blades of grass of his meadow, even every individual weed which grows among the grain of his field and the useful plants of his garden; for these also, regarded from the physiological point of view, belong to the "total production" of the ground. And what would be gained by all these immense countings? Just as little as with the "desolate figures" in Henseu's long numerical protocols. *

VOLUME AND WEIGHT OF THE PLANKTON.

If one actually regards the determination of the planktonic yield as a highly important subject, and believes that this can be solved by a certain number of quantitative plankton analyses, then this goal can be reached in the simplest way by determination of the volume and weight of each planktonic catch. Heusen himself naturally first trod this nearest way; but he thinks that it is not accurate enough and encounters difiiculties (9, p. 15). In his opinion, "an accurate analysis of the plankton, on account of the great variety of its parts, can only be obtained by counting; he quite forgets that such a counting of individuals also possesses only an approximate and relative value, not a complete and absolute one; farther, that from the counting of the difierent individuals no more certain measure for the economic value of the whole diversely constituted i)lanktonic catch is furnished finally that the counting of one catch is of highest value as a single factor of a great computation, which is made from thousands of dif- ferent factors. The only thorough method of determining the yield, in plauktology as in economy, is the determination of the useful substance according to mass and weight and subsequent chemical analysis. In fact, the determination of the planktonic volume, as of the weight, just as the qualitative and (piantitative chemical analysis of the plankton, is pos- sible up to a certain degree. The difficulties are less than Hensen believes. It seems odd that the latter has not mentioned tbese two simplest methods in a single place in his comprehensive volume (9, p. 15), but hastily casts them aside and replaces them with the quite use- less " counting of individuals," a Danaid^e task of many years.

*'\\niile Hensen is going over the connting of the single constituent parts of the plankton, he calls special attention to the fact ''that iii spite of the apparently" desolate figures, in almost every single case certain results of general interest have come out, though the opportunity is not offered to show thena in a comparison. PLANKTONIC STUDIES. 635

CYCLE OF MATTER IN THE OCEAN {Stoffwcchscl des Meeres.)

The many and great questions which the mighty cycle of matter in the ocean furnishes to biology, the questions of the source of the fun- damental food supply, of the reciprocal trophic relations of the marine flora and fauna, of the conditions of support of tlie bentbonic and planktonic organisms, etc., have, within the last twenty years, since

the beginning of the epoch-making deep-sea investigation (13), been much discussed and have received very different answers (11). Hen- sen has also devoted considerable attention to this, and particularly emphasizes the physiological importance of the fundamental food sup-

ply ( Urnahrung). He believes this complicated question can be solved esi)ecially by quant it at ice determination of the fiin(Jamcntal food stippli/. I have already shown why this method of quantitative plankton analysis must be regarded as useless. Even assuming that it were possible and practicable, I can not understand how it could lead to a definite solution of this question. On the other hand, I might here point to one side of the oceanic cycle of matter whose further pursuit seems very profitable. The two chief sources of the "oceanic fun- damental food supply" have already been correctly recognized by

Mobius (11), Wyville Thompson (13, 14), Murray (6), and others: First, the vast terrigenous masses of organic and particularly vegetable substances, which are daily brought by the rivers to the sea; sec- ondly, the immense quantities of plant food which the marine flora itself furnishes. Of the latter we previously had in mind chiefly the benthonic littoral flora, the mighty forests of alga', meadows of Zostera, etc., which grow in the coast waters. ;Only in recent times have we learned to value the astonishing quantity of vegetable food which the planktonic flora i^roduces, the Fiicoids of the Sargasso Sea on the one side, the Oscillatoriw and the microscopic Diatoms and Peridinew on the other. But the smaller groups of i^elagic Protophytes^ which I have mentioned above, the Ghromacete^ Murracytecc, Xantliellece, Divtyochece, etc., also play an importantTole. Tlie great importance which devolves upon the small symbiotic XantJieUea\ has been especially emphasized by Brandt (24), Moseley (7), and Geddes. Evidently their multiplica- tion is extremely rapid, and if each second milliard of such Protophytes were eaten by small animals, new milliards would take their places. \Yli6ther or not the number of these milliards is shown to us by the quantitative planktonic analysis seems to me wholly indifferent. More important for the understanding of their j)hysiological importance would be the ascertainment of the rapidity of the increase. The importance of these Protophytes and of the Protozoa living ujion thein has lately been particularly described by Chun (28, pp. 10, 13). He has also rightly emphasized the extraordinary importance which the vertical m igration of the bathy])elagic animals has for the support of the deep-sea animals. They are to a great extent the under workmen, who 636 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

constantly bring- the provision transports into the deep sea (15, pp. 49, 57). Thither, in addition, come the immense quantities of marine plant and animal corpses, which daily sink into the depths and are borne away by currents. Thither comes the constant "rain" of the corpses of zonary Protozoa (especially Glohigerina and RafUoIaria), which uninterruptedly pour down through all the zones of depth into the deepest abysses, and whose shells form the most abundant sediment of the deep sea, the calcareous Glohigerina ooze and the siliceous Radiolaria ooze. In general, it seems to me that the daily supply of food materials which the decaying corpses of numberless marine organisms furnish to the others, is much more important than is commonly supposed.* How much food would a single dead whale alone furnish? But especially important and not sufficiently valued in this regard it seems to me, is the trophic importance of the benthos for the plankton. Immense quantities of littoral benthos are daily carried out into the ocean by the currents. Here they soon disappear, since they serve as food for the organisms of the phmkton. If one weighs all these com- plicated reciprocal relations, he obtains without counting- a sufficient general conception of the "cycle of the organic material in the marine world."

COMPARATIVE AND EXACT METHODS.

The farther the two great branches of biology, namely, morphology and physiology, have developed into higher planes during the last decade, so much tiirther have the methods of investigation in both sciences diverged from one anothei-. In morphology the high worth of comparative or declarant methods has always been justly more recog- nized, since the general phenomena of structure {e. g., in ontogeny and system ization) have been in great part removed from exact investi- gation, and comprise historical problems, the solution of which we can strive for only indirectly (by way of comparative anatomy and phylo- genetic speculation). In physiology, on the -other hand, we constantly strive to employ the exact or mathematical methods, Avhich have the advantage of relative accuracy and which enable us to trace back the general phenomena, of vital activity directly to physical (particularly to chemical) processes. Plainly it must be the endeavor of all sciences (of morphology also) to find and retain as much as possible this exact mode of investigation. But it is to be regretted that among most branches of science (and particularly the biological ones) thisls not possible, because the empirical foundations are much too incomplete and

*Heu8en values this source of food very slightly, because "only a very few aui- malslive upon dead matter," and explains it iu this way, "that material in a state of foul putrefaction requires a stronger digestive power than the organization of the lower animals can produce " (9, p. 2). I must contradict both ideas. The sponges live chiefly upon decaying organisms, as do also many Protozoa, Helminths, Crustacea, etc. PLANKTONIC STUDIES. 637 tUe problems in hand iiiiu-U too coinplicated. >ratliematical treatment of these does more liarm tlian good, betuiuse it tjives a deceptive sem- l)lauce of accuracy, which in fact is not attainable.* A part of physi- ology also embraces such subjects as are with difficulty, or even not at all, accessible to exact definition, and to these also belong the chorology and (ecology of the plankton. The funda mental fault of Tlenseii^^ plankton tJieori/ in my opinion lies in the fact that he regards a highly complicated i)roblem of biology as a relatively simple one, that he regards its many oscillating- parts as pro])ortlonally constant bulks, and that he believes that a knowledge of these can be reached by the exact method of mathematical counting and computation. This error is partly excusable from the circum- stance that the i»hysiology of to-day, in its one-sided pursuit of exact research, has lost sight of many general problems which are not suited for exact special investigation. This is shown esi)ecially in the case of the most important question of our i)resent theory of develop- ment, the species jjroblem. The discussions which Ilensen gives upon the nature of tlie species, u})on systemization, Darwinism, and the descent theory, in many places in his plankton volume (pp. 19, 41, 7o, etc) are among the most peculiar v/hich the volume contains. They deserve the special attention of the systematist. The "actual species" is for him a physiological conception, while, as is known, all distinction of species has hitherto been reached by morphological means.t In my Report on the Badiolaria of H, M. S. Challenger I have at- tempted to point out how the extremely manifold forms of this most numerous class (739 genera and 4,.'U8 species) are on the one hand dis- tinguished as species by morphological characters, and yet on the other hand may be regarded as modifications of 85 family types, or as de- scendants of 20 ancestral orders, and these again as derived from one common simple ancestral form {Actis.saj 4, § loS). Hensen on the other hand is of the opinion that therein is to be found "a strong opposing proof against the independence of the species" (9, j). 100). He hopes

"to lighten the systematic difiiculties by the help of computation" (p. 75). Through his systematic plankton investigations he has reached

* A familiar and very iustrtictive t'xauii)l(i of this perverted employment of exact methods in morphblogy is furnislied by the familiar "Mechanical theory of develop- ment" of His, which I have examined in my anthropogeny (3d edition, p. 53, 655) as well as in my paper upon Ziclc and Wege dcr Entwickehingsgeschichte (Jena, 1875).

t Since of late the physiological importance of the "species" concci)tiou has often been emphasized and the " system of the futnre " by the way of '•' comparative physi- ology " has been pointed out, it must here be considered that np to this time not one of these systematic physiologists has given even a hint how this new system of description of species can be practically carried out. What Hensen has said about it (i», pp. 41, 73, 100) is just as worthless as the earlier discussions by Pol^jaeff, which have been critically considered in my Report on the Deep-Sea Kerafcosa {Challenger, Zoology, vol. XXXII, part 82, pp. 82-85.) G38 EEPORT OP COMMISSIONER OF FISH AND FISHERIES. the conviction tluit '' the more accurately tlie investigation lias been made, so much tlie more plain becomes the distinction of species" (9, p. 100), On the other side I, like Charles Darwin, through many years of comparative and systematic work, have arrived at the opposite con- clusion: " The more accurately the systematic incestUjations are made, the greater the number of individ^tals of a S2)fcies compared^ the intenser the study of individual variation, hy so much more impossible becomes the distinction of actual species, so much more arbitrary the subjective Uuiits of their extent, so much stronger the conviction of the truth of the Theory of Descent.'^* PLANKTOLOGICAL PROBLEMS.

The wonderful world of organic life, which fills the vast oceans, offers a fund of very interesting subjects. Without question, it is one of the most attractive and profitable fields of bioh)gy. If we consider that the greater part of this field has been open to us scarcely fifty years, and if we wonder at the new discoveries which the Challenger expedition alone has brought to light, then we ought to count iipon a brilliant future for planktology. Above all we ought to cherish the hope that our German National expedition, the first great German undertaking in the field, may promote many x>lanktonic problems, and that the six naturalists who, under such favorable conditions and with such important instruments, studied the oceanic plankton for ninety-three days and in 400 hauls of the net were able to ol)tain a rich collection of pelagic organisms, will by their careful working up of these enrich our knowledge many fold. However, the preliminary contributions of Hensen (22) and Brandt (23) give us no means of passing judgment ni^on the matter now. Among the results which the former has briefly given to the Bejlin Academy few require consideration; but for this the difference of our general ])oint of view is to blame. Thus, for exami)le, I have attempted to explain the remarkable "similarity to water of the pelagic fauna," the transparency of the colorless glassy animals, in 1860, in iny General Morphology (ii, p. 242), according to Darwin's Theory of Selection, by natural selection of like colors (30, p. 248). Hensen, on the other hand,

* F. Heincke lias briefly, in his careful "Investigations npon' the Stickleback," " given expression to the same conviction in the following words : All the conclu- sions here deduced by me are simply and solely I'ounded upon the comparison of very many individuals of living species, or, in other words, upon the study of indi- vidual variation. I am convinced that in essentials the study of embryology will conlirm my theory. It will be a proof of this, that he who wishes accurately to describe related species, and races of a species, and to study their genealogical rela- tion to one another, must begin by comparing a very {ircat number of ifidividuals from different, localities accurately and methodically. He will then soon see thai proofs of the theory of descent by tliis means are found in great nmnbers at all times, if only one docs not spare the pains to trace them out." (Ofversigt af K. V. Akad. Forh. Stock- holm, 1889, No. 6, p. 410.) This view of Heincke is shared by every experienced ami unbiased svetcmatist. PLANKTONIC STUDIES. 639 regards Imiiger as the cause of this, uud the "teiuleucy to explore a rehitively great bulk of water." In general, according to his view, " many larger pelagic aninuils bear the outsi)oken character of unfavor- able conditions of life, of a life of hunger." Eegarding the appearance of many i^elagic animals in swarms, Hensen explains " that the young do not float, but swim freely. In conse(iuence of this, the mother animals drive tirem away, and if the larva', linally rise to the surface the former can not enter into competition with

them" (23, p. 252). The accumulation of numbers of FlujsaHa in great swarms stands, according to his view, in correlation with the mode ot movement. The animals which are capable of no independent move- ment of progression must renmiu rather closely crowded together, in order to be able to reproduce hisexnaJUj; those carried too far away must perish." On the other hand it is to be noted that the Physalia is not, as Hensen assumes, go)iochoristic, but always hermaphroditic* The above-mentioned phenomena, the similarity to water of the pe- lagic fauna, the periodic appearance of many pelagic organisms in swarms, their abundant accumulation in the zoi (currents (p. 85), particu- larly their relation to the currents, are only a few of the greater prob- lems which planktology furnishes for human investigative energy. For these, as for so many other fields of biology, Charles Darwin, by the establishment of the descent theory, has opened to us the way to a knowledge of causes. We must study the complicated reciprocal relations of the organisms crowded together in the struggle for exist- ence, the interaction of heredity and variation, in order to learn to understand the life of the plankton. But in these plankton studies, as well in physiological as in morphological questions, we nuist use that method Avhich Johannes Miiller, the discoverer of this field, always employed in a manner worthy of imitation: simultaneous "observation and reflection."

* The cormi of all Physalida; are moua-cions, their cormidia monoclinic. ICach siu"-le brancli of the racemose gonodcudron is niunostylic, and hears one female and several male medusoids. The facts were brought out thirty -five years ago by Huxley. Challenger, vol. xxviii, (Compare my Keport ou the SiphouophoriC : Zoology of the pp. 347, 356.) 640 REPORT OF COMMISSIONER OF FISH AND FISHERIES.

LITERATURE.

1. Johannes ^Mullek. 1845-1855. Ucher die Larven nnd die Metamorpho.se der Echi- noderuieii. A))liandluugen der Berliner Akadeaiie der Wis.senschaften.

2. , 1858. Ueber dieThassicollen, I'olycystiiien uud Acautboiiietreii des Mit- telmeeres. Idem.

3. Ernst H.eckel, 1862. Monographie der Kadiolarieu. Uebersicht der Verbrei-

tung, i)p. 166-193.

4. , 1887. Report ou the Radiolaria collected by II. M. S. Challeuger dtiriug

the year.s 1873-187G. Chronological .section. §iji 226-240. (Deutsch' in der "Allgemeineu Naturgeschichte der Radiolarieu." 1887, jip. 123-137.)

5. John Murray, 1876. Preliminary report ou some surface organisms examined on board II. M. S. Challenger, and their relation to ocean deposits. Proceed. Roy. Soc, vol. xxiv, pp. 532-,5.S7.

6. , 1885. Narrativeof crui.se of H. M. S. Challenger, with a general account

of the scientific i-esults of the expedition (1873-1876), vol. i, li.

7. H. N. MOSELEY, 1882. Pelagic Life. Address at the Southampton Meet. Brit. Assoc, Nature, vol. xxvi, No. 675, p. 559.

8. Gaetano Chiercuia, 1885. C(dlezi(mi per Stud i di Scienze Natural i, fa tteuel Viaggio intorno al moudo dalla R. corvetta Vettor Pisani. Anni 1882- 1885.

9. Victor Hensex, 1887. Ueber die Bestimmung des Planktons, oder des im Meere treibendcn Materials an Pflanzeu und Thieren. Y. Bericht der Commis- sion zur wissensch. Unters. der Deutschen Meere in Kiel. 10. K. MoBius, 1887. Systematische Darstellung der Thiere des Plankton in der westl. Ostsee uud auf einer Fahrfc von Kiel in den Atlantischeu Ocean bis jenseit der Hebriden. (V. Idem).

11. , 1871. Wo kommt die Nahrung fiir die Tiefseethiere her? Zeitsch. fiir wissensch. ZooL, 21. Bd., p. 294. 12. Th. Fuchs, 1882. Ueber die pelagische Flora uud Fauna. Verhaudl. d. k. k. Geolog. Reichsanstalt iu Wien, 4. Febr., 1882, pp. 49-.55. 13. Wyville Thoaipson, 1873. The Depths of the Sea. An account of the general results of the dredging cruises of H. M. S. S. Porcupine and Lightniug.

14. , 1877. The Atlantic. A preliminary account of the general results of the exploring voyage of H. M. S. Challenger. 15. Carl Chi'X, 1888. Die pelagische Thierwelt in grosseren Meerestiefen uud ihre

Beziehungeu zu der Oljerfliichen-Fauna. Bibliotheca zoologica. Heft i.

16. , 1889. Bericht iiber eiue nach den Canarischen Inseln im Winter 1887-88 ausgefiihrte Reise. Sitzungsberichte der Berliner Akadeniie der Wiss., p. 519. 17. Carl Vogt, 1848. Ocean uud Mittelmeer, p. 303. 18. Richard Greeff, 1868. Reise nach deu Canarischen luselu. " Die Meeresstro- mungen als Thierstrassen," pp. 307-309. 19. R. ScriiMiDTLEiN, 1879. Vergleichende Uebersicht iiber das Ersclieineu grosserer pelagischer Thiere wiihreud der Jahre 1875-1877. Mittheil der zoolog.

Station Neapel, Bd i, p. 119. 20. Edward Gkaekee, 1881-88. Uebersicht der Seethier-Fauna des Golfes von Triest, nebst Notizeu iiber Vorkommen, Lebensweise, Erscheinungs- und Fortpflauzungs-Zeit. Arbeiten d. zool. Station Triest. 21. E. i>u Bo*s-Reymond, 1890. Bericht iiber die Huraboldt-Stiftung und die Kieler Plankton-Expedition des National. Sitzungslierichte der Berliner Akademie d. Wissensch. vom 23. Januar 1890, pp. 83-87. I'LANKTONIC STUDIES. 641

22. Victor Hensex, 18il0. P^inige Ergelinisse der Plankton-Expeditiou der Hiim- boldt-Stiftiing. Sitzniigsberichte der Berliner Akaderaie der Wisseu- schaffcen voin 13. Miirz 1890, pp. 243-253. 23. K.\RL Bkandt, 1889. Ueber die biologischen irntersuchungen der Plankton-Ex-

jieditiou. Verhandl. der GeselLschaft fiir Erdkimde zu Berlin, vom 7. Dec. 1889, p. 515.

24. , 1885. Die coloniebilden

29. Ernst H^CKEL, 1879. Monogrnphie derMednsen. I. Bd. Das System der Medu- sen, II. Bd. Der Orgauismus der Meduseu.

30. , 1889. Natiirlicbe Schopfimgsgescbichte. Aclite AuJiage.

H. Mis. 113 41